41 lines
1.8 KiB
Markdown
41 lines
1.8 KiB
Markdown
# Permit `stackalloc` in nested contexts
|
|
|
|
### Stack allocation
|
|
|
|
We modify the section [*Stack allocation*](https://github.com/dotnet/csharplang/blob/master/spec/unsafe-code.md#stack-allocation) of the C# language specification to relax the places when a `stackalloc` expression may appear. We delete
|
|
|
|
``` antlr
|
|
local_variable_initializer_unsafe
|
|
: stackalloc_initializer
|
|
;
|
|
|
|
stackalloc_initializer
|
|
: 'stackalloc' unmanaged_type '[' expression ']'
|
|
;
|
|
```
|
|
|
|
and replace them with
|
|
|
|
``` antlr
|
|
primary_no_array_creation_expression
|
|
: stackalloc_initializer
|
|
;
|
|
|
|
stackalloc_initializer
|
|
: 'stackalloc' unmanaged_type '[' expression? ']' array_initializer?
|
|
| 'stackalloc' '[' expression? ']' array_initializer
|
|
;
|
|
```
|
|
|
|
Note that the addition of an *array_initializer* to *stackalloc_initializer* (and making the index expression optional) was an [extension in C# 7.3](https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.3/stackalloc-array-initializers.md) and is not described here.
|
|
|
|
The *element type* of the `stackalloc` expression is the *unmanaged_type* named in the stackalloc expression, if any, or the common type among the elements of the *array_initializer* otherwise.
|
|
|
|
The type of the *stackalloc_initializer* with *element type* `K` depends on its syntactic context:
|
|
- If the *stackalloc_initializer* appears directly as the *local_variable_initializer* of a *local_variable_declaration* statement or a *for_initializer*, then its type is `K*`.
|
|
- Otherwise its type is `System.Span<K>`.
|
|
|
|
### Stackalloc Conversion
|
|
|
|
The *stackalloc conversion* is a new built-in implicit conversion from expression. When the type of a *stackalloc_initializer* is `K*`, there is an implicit *stackalloc conversion* from the *stackalloc_initializer* to the type `System.Span<K>`.
|