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Document insert() and erase() of editable json_documents
Add API reference pages for basic_json_document::insert and basic_json_document::erase, matching the style of set.md and push_back.md: signatures, parameters, return values, exception safety, exceptions with their exact ids and messages, complexity, notes on duplicate keys and view/iterator validity, and an example. Add example programs basic_json_document__insert.cpp and basic_json_document__erase.cpp with their expected output, each comparing an edit on an editable document with the same edit on a plain json value to show what is preserved: member order, the spelling of untouched numbers, and, for insert, that a view taken before the insert keeps referring to the same element after its index shifts. Register both new pages in mkdocs.yml, docSet.sql, and the member list of basic_json_document/index.md, add cross-references to them from set.md and push_back.md, and mention insert/erase in the "Editing a document" section of features/json_view.md. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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Niels Lohmann
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# <small>nlohmann::basic_json_document::</small>erase
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```cpp
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// (1)
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std::size_t erase(view_type object, string_view_t key);
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// (2)
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template<typename I>
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void erase(view_type array, I idx);
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// (3)
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std::size_t erase(const json_pointer& ptr);
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```
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Only an **editable** document (`#!cpp Editable == true`, e.g. [`json_editable_document`](../json_editable_document.md))
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has `erase`; calling it on a read-only `basic_json_document` fails to compile (`#!cpp static_assert`).
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1. Removes every member of `object` whose key is `key` (see [Notes](#notes) on duplicate keys) and returns how many
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were removed; `#!cpp 0` if `object` has no member with this key.
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2. Removes the element at index `idx` of `array`, which must already exist (`#!cpp idx < array.size()`).
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3. Removes the value the JSON pointer `ptr` refers to, relative to [`root()`](root.md), and returns how many values
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were removed: the *parent* of the target must already exist, and the target itself is removed as in 1. (an object
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member; `#!cpp 0` or more) or 2. (an array element; always `#!cpp 1`). `ptr` must not be empty -- [`root()`](root.md)
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itself cannot be erased.
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## Template parameters
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`I`
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: an integral type other than `#!cpp bool`, deduced (overloads taking a `#!cpp bool` or a non-integral type for
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`idx` do not participate in overload resolution).
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## Parameters
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`object` (in)
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: the object to remove a member of
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`array` (in)
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: the array to remove an element of
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`key` (in)
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: the key of the member(s) to remove
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`idx` (in)
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: the index of the element to remove; a negative value throws (see [Exceptions](#exceptions))
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`ptr` (in)
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: a JSON pointer to the value to remove, relative to `root()`
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## Return value
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1. the number of removed members (`#!cpp 0` if `object` had none with this `key`)
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2. (nothing)
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3. the number of removed values (`#!cpp 0` or more for an object member, always `#!cpp 1` for an array element)
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## Exceptions
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1. Throws [`type_error.307`](../../home/exceptions.md#jsonexceptiontype_error307) if `object` is not an object -- the
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same message [`BasicJsonType::erase`](../basic_json/erase.md) throws for the same type.
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2. Throws `type_error.307` if `array` is not an array. Throws
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[`out_of_range.401`](../../home/exceptions.md#jsonexceptionout_of_range401) if `idx` is negative, or if
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`#!cpp idx >= array.size()`.
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3. Throws [`out_of_range.405`](../../home/exceptions.md#jsonexceptionout_of_range405) ("JSON pointer has no parent")
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if `ptr` is empty. Throws what [`at`](../basic_json_view/at.md) throws (overload 3) for resolving `ptr`'s parent.
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For the last reference token itself: if the parent is an array, throws what 2. throws for an index that is out of
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range, or, for a token that is not a valid array index,
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[`parse_error.106`](../../home/exceptions.md#jsonexceptionparse_error106) (a leading `#!cpp '0'`),
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[`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) (not a number),
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[`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) (too large for `size_type`), or
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[`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) (an empty token); otherwise (an
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object, or a primitive value the pointer's parent resolves to) throws what 1. throws.
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Every overload also throws [`invalid_iterator.202`](../../home/exceptions.md#jsonexceptioninvalid_iterator202) ("view
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does not belong to this document") if `object`/`array` is a [discarded](../basic_json_view/is_discarded.md) view or a
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view of a *different* document (overloads 1-2 only; overload 3 always starts from this document's own
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[`root()`](root.md)).
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## Complexity
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1. Linear in the number of members of `object`.
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2. Linear in the number of elements of `array` at or after `idx` (they move one slot over).
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3. Linear in the number of reference tokens of `ptr` and, for each token, in the number of members of the object at
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that level or the index into the array (as [`at`](../basic_json_view/at.md)), plus the complexity of 1. or 2. for
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the last token.
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## Notes
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!!! info "Duplicate keys"
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Overload 1. removes *every* member with `key`, not just the first -- unlike [`set`](set.md), which assigns the
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first occurrence and drops the rest. This is why it returns a count rather than a single view: there may be
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more than one member removed, or none.
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Like [`set`](set.md) and [`push_back`](push_back.md), `erase` never moves an element's *value*: a view still
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referring to a removed member or element keeps showing what it last held (see [Edits](index.md#edits)) -- it just no
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longer appears when `array`/`object` is read, dumped, or iterated. Removing an element of `array` (2.) does shift the
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*links* to the elements after it, the same way `insert`, `set`, or `push_back` on the same array would; any iterator
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already taken over `array`/`object` is invalidated by an erase, since it was walking the old layout.
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## Examples
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??? example
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The example below drops a deprecated field and a decommissioned entry from a configuration document -- using all
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three overloads -- and shows what stays intact that would not with a plain `json`/`ordered_json` value: the order
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of the fields around the ones removed, and the exact spelling of a number that was never touched.
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```cpp
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--8<-- "examples/basic_json_document__erase.cpp"
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```
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Output:
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```json
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--8<-- "examples/basic_json_document__erase.output"
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```
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## See also
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- [insert](insert.md) - insert an element into an array
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- [set](set.md) - replace a value, or set an object member, an array element, or the value a JSON pointer refers to
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- [push_back](push_back.md) - append to an array
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- [root](root.md) - the view of the root value, the starting point of overload 3
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- [`BasicJsonType::erase`](../basic_json/erase.md) - the corresponding function of `basic_json`
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- [Edits](index.md#edits) - what an edit guarantees, for every overload
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## Version history
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- Added in version 3.13.0.
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@@ -19,10 +19,10 @@ it (a copy, or an rvalue `#!cpp std::string` that was moved in); see [`owns_sour
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is move-only: copying a document would either duplicate a potentially large index and text, or leave two documents
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claiming to borrow the same buffer, so it is disabled.
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With `#!cpp Editable == true`, the document also offers [`set`](set.md) and [`push_back`](push_back.md) to change
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values in place, see [Edits](#edits) below. The source text itself is never written; a read-only document
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(`#!cpp Editable == false`, the default) does not carry any of the bookkeeping edits need, and calling `set` or
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`push_back` on one fails to compile (`#!cpp static_assert`).
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With `#!cpp Editable == true`, the document also offers [`set`](set.md), [`push_back`](push_back.md),
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[`insert`](insert.md), and [`erase`](erase.md) to change values in place, see [Edits](#edits) below. The source text
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itself is never written; a read-only document (`#!cpp Editable == false`, the default) does not carry any of the
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bookkeeping edits need, and calling any of them on one fails to compile (`#!cpp static_assert`).
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## Template parameters
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@@ -32,8 +32,8 @@ values in place, see [Edits](#edits) below. The source text itself is never writ
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is checked with a `static_assert`.
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`Editable`
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: whether the document supports [`set`](set.md) and [`push_back`](push_back.md) (optional, `#!cpp false` by
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default). See [Edits](#edits) below.
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: whether the document supports [`set`](set.md), [`push_back`](push_back.md), [`insert`](insert.md), and
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[`erase`](erase.md) (optional, `#!cpp false` by default). See [Edits](#edits) below.
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## Specializations
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@@ -66,11 +66,15 @@ values in place, see [Edits](#edits) below. The source text itself is never writ
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- [**set**](set.md) - replace a value, or set an object member, an array element, or the value a JSON pointer refers
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to (`#!cpp Editable` documents only)
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- [**push_back**](push_back.md) - append to an array (`#!cpp Editable` documents only)
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- [**insert**](insert.md) - insert an element into an array before a given position (`#!cpp Editable` documents only)
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- [**erase**](erase.md) - remove an object member, an array element, or the value a JSON pointer refers to
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(`#!cpp Editable` documents only)
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## Edits
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An editable document (`#!cpp Editable == true`) can be changed after parsing, with [`set`](set.md) and
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[`push_back`](push_back.md); [`json_editable_document`](../json_editable_document.md) and
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An editable document (`#!cpp Editable == true`) can be changed after parsing, with [`set`](set.md),
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[`push_back`](push_back.md), [`insert`](insert.md), and [`erase`](erase.md);
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[`json_editable_document`](../json_editable_document.md) and
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[`ordered_json_editable_document`](../ordered_json_editable_document.md) are the corresponding specializations. A few
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points apply to every edit:
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@@ -0,0 +1,114 @@
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# <small>nlohmann::basic_json_document::</small>insert
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```cpp
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template<typename I, typename V>
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view_type insert(view_type array, I idx, V&& value);
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```
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Only an **editable** document (`#!cpp Editable == true`, e.g. [`json_editable_document`](../json_editable_document.md))
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has `insert`; calling it on a read-only `basic_json_document` fails to compile (`#!cpp static_assert`).
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Inserts `value` into `array` as a new element before position `idx`, which must not be past the end
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(`#!cpp idx <= array.size()`; `#!cpp idx == array.size()` appends, like [`push_back`](push_back.md)). Unlike
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[`push_back`](push_back.md), a [null](../basic_json_view/is_null.md) `array` does *not* first become an empty array:
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`array` must already be an array.
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`value` is accepted three ways: a [`basic_json_view`](../basic_json_view/index.md) of *any* document -- read-only or
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editable, and it does not have to be `array`'s own document -- which is copied so that nothing is shared with the
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source document afterward; a `BasicJsonType` value; or anything `BasicJsonType` can be constructed from (numbers,
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strings, `#!cpp bool`, `#!cpp nullptr`, containers, ...).
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## Template parameters
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`I`
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: an integral type other than `#!cpp bool`, deduced (overloads taking a `#!cpp bool` or a non-integral type for
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`idx` do not participate in overload resolution).
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`V`
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: the type of `value`, deduced; see above for what is accepted.
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## Parameters
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`array` (in)
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: the array to insert into
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`idx` (in)
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: the position to insert `value` before; a negative value throws (see [Exceptions](#exceptions))
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`value` (in)
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: the value to insert
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## Return value
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a view of the new element, now holding `value`
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## Exception safety
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Basic exception safety: `value` is fully encoded -- including the checks below -- into storage owned by the document
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before anything already reachable from [`root()`](root.md) is touched, so a failure while encoding `value` (an
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invalid argument, or `#!cpp std::bad_alloc`) leaves the document completely unchanged, other than memory allocated
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for the encoding that is not reclaimed. A failure of a later allocation -- while `array` switches from its parsed
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layout to a growable block, or while that block grows, see [Notes](#notes) -- can still leave `array` already
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switched to that layout even though `value` itself was not inserted.
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## Exceptions
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Throws [`type_error.309`](../../home/exceptions.md#jsonexceptiontype_error309) if `array` is not an array -- the same
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message [`BasicJsonType::insert`](../basic_json/insert.md) throws for the same type; a null `array` throws this too
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(see above). Throws [`out_of_range.401`](../../home/exceptions.md#jsonexceptionout_of_range401) if `idx` is negative,
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or if `#!cpp idx > array.size()`. Throws
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[`invalid_iterator.202`](../../home/exceptions.md#jsonexceptioninvalid_iterator202) ("view does not belong to this
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document") if `array` is a [discarded](../basic_json_view/is_discarded.md) view or a view of a *different* document.
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Throws [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) if `value` is a
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[discarded](../basic_json_view/is_discarded.md) view or a [discarded](../basic_json/is_discarded.md) `BasicJsonType`
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value, and [`type_error.319`](../../home/exceptions.md#jsonexceptiontype_error319) if `value` is (or contains) a
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binary value -- `BasicJsonType` can hold one, but a `json_document` cannot. Throws
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[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) if `value` is (or contains) a string that is
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not valid UTF-8, with the same message [`BasicJsonType::dump()`](../basic_json/dump.md) gives for that string.
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## Complexity
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Linear in the number of elements of `array` at or after `idx` (they move one slot over), plus time linear in the
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size of `value` to encode it into the document's storage (constant for a scalar, linear in the number of nested
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values for an array or object): like [`push_back`](push_back.md), the elements of `array` move to a growable block
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of links the first time it is inserted into (or [`set`](set.md)/[`push_back`](push_back.md) on), and that block
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grows in amortized constant time; inserting before the end within that block still shifts every later element.
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## Notes
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Like [`set`](set.md) on a member or an element, `insert` never moves an existing *element's value* -- only where
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`array`'s *links* to its elements live -- so a view of an existing element of `array` stays valid across an
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`insert`, and keeps referring to the same element even though its index shifts. Any iterator already taken over
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`array` is invalidated, since it was walking the old layout. See [Edits](index.md#edits) for what stays valid across
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an edit in general.
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## Examples
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??? example
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The example below inserts a step into the middle of a deployment plan, without touching the steps that come
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after it, and shows that a view taken before the insert keeps referring to the same element even though its
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index shifts -- something a plain `json`/`ordered_json` array, or its `std::vector`-based storage, has no
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equivalent for.
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```cpp
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--8<-- "examples/basic_json_document__insert.cpp"
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```
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Output:
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```json
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--8<-- "examples/basic_json_document__insert.output"
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```
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## See also
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- [push_back](push_back.md) - append to an array
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- [erase](erase.md) - remove an object member, an array element, or the value a JSON pointer refers to
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- [set](set.md) - replace a value, or set an object member, an array element, or the value a JSON pointer refers to
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- [`BasicJsonType::insert`](../basic_json/insert.md) - the corresponding function of `basic_json`
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- [Edits](index.md#edits) - what an edit guarantees, for every overload
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## Version history
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- Added in version 3.13.0.
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@@ -91,6 +91,8 @@ Like [`set`](set.md) on a member or an element, `push_back` never moves an exist
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## See also
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- [set](set.md) - replace a value, or set an object member, an array element, or the value a JSON pointer refers to
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- [insert](insert.md) - insert an element into an array before a given position
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- [erase](erase.md) - remove an object member, an array element, or the value a JSON pointer refers to
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- [root](root.md) - the view of the root value
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- [`BasicJsonType::push_back`](../basic_json/push_back.md) - the corresponding function of `basic_json`
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- [Edits](index.md#edits) - what an edit guarantees, for every overload
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@@ -180,6 +180,8 @@ one-node scalar.
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## See also
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- [push_back](push_back.md) - append to an array
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- [insert](insert.md) - insert an element into an array
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- [erase](erase.md) - remove an object member, an array element, or the value a JSON pointer refers to
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- [root](root.md) - the view of the root value, the starting point of overload 4
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- [`basic_json_view::dump`](../basic_json_view/dump.md) - serialize the document, keeping an untouched number's
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spelling with `#!cpp number_format::source`
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