Ordinary arrays can be created through the following syntax: ```C# new int[3] new int[3] { 1, 2, 3 } new int[] { 1, 2, 3 } new[] { 1, 2, 3 } ``` We should allow stack allocated arrays be created through: ```C# stackalloc int[3] // currently allowed stackalloc int[3] { 1, 2, 3 } stackalloc int[] { 1, 2, 3 } stackalloc[] { 1, 2, 3 } ```
1.9 KiB
Stackalloc array initializers.
- Proposed
- Prototype: Not Started
- Implementation: Not Started
- Specification: Not Started
Summary
Allow array initializer syntax to be used with stackalloc
Motivation
Ordinary arrays can have their elements initialized at creation time. It seems reasonable to allow that in stackalloc
case.
The question of why such syntax is not allowed with stackalloc
arises fairly frequently.
See, for example, https://github.com/dotnet/csharplang/issues/1112
Detailed design
Ordinary arrays can be created through the following syntax:
new int[3]
new int[3] { 1, 2, 3 }
new int[] { 1, 2, 3 }
new[] { 1, 2, 3 }
We should allow stack allocated arrays be created through:
stackalloc int[3] // currently allowed
stackalloc int[3] { 1, 2, 3 }
stackalloc int[] { 1, 2, 3 }
stackalloc[] { 1, 2, 3 }
The semantics of all cases is roughly the same as with arrays.
For example: in the last case the element type is inferred from the initializer and must be an "unmanaged" type.
NOTE: the feature is not dependent on the target being a Span<T>
. It is just as applicable in T*
case, so it does not seem reasonable to predicate it on Span<T>
case.
Translation
The naive implementation could just initialize the array right after creation through a series of element-wise assignments.
Similarly to the case with arrays, it might be possible and desirable to detect cases where all or most of the elements are blittable types and use more efficient techniques by copying over the pre-created state of all the constant elements.
Drawbacks
Alternatives
This is a convenience feature. It is possible to just do nothing.
Unresolved questions
Design meetings
None yet.