stackalloc在嵌套上下文中允许Permit stackalloc in nested contexts

  • 项目

堆栈分配Stack allocation

我们修改 c # 语言规范的部分 堆栈分配 ，以便在 stackalloc 可能出现表达式时放松位置。We modify the section Stack allocation of the C# language specification to relax the places when a stackalloc expression may appear. 我们删除We delete

local_variable_initializer_unsafe
    : stackalloc_initializer
    ;

stackalloc_initializer
    : 'stackalloc' unmanaged_type '[' expression ']'
    ;

并将其替换为and replace them with

primary_no_array_creation_expression
    : stackalloc_initializer
    ;

stackalloc_initializer
    : 'stackalloc' unmanaged_type '[' expression? ']' array_initializer?
    | 'stackalloc' '[' expression? ']' array_initializer
    ;

请注意，将 array_initializer 添加到 stackalloc_initializer (并使索引表达式可选) 是 c # 7.3 中 的一个扩展，此处未进行描述。Note that the addition of an array_initializer to stackalloc_initializer (and making the index expression optional) was an extension in C# 7.3 and is not described here.

表达式的 元素类型 stackalloc 是 stackalloc 表达式中命名的 unmanaged_type （如果有），或者 array_initializer 的元素中的通用类型，则为; 否则为。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.

具有 元素类型 的 stackalloc_initializer 的类型 K 取决于其语法上下文：The type of the stackalloc_initializer with element type K depends on its syntactic context:

  • 如果 stackalloc_initializer 直接显示为 local_variable_declaration 语句或 for_initializer 的 local_variable_initializer ，则其类型为 K* 。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*.
  • 否则，它的类型为 System.Span<K> 。Otherwise its type is System.Span<K>.

Stackalloc 转换Stackalloc Conversion

Stackalloc 转换 是来自 expression 的新的内置隐式转换。The stackalloc conversion is a new built-in implicit conversion from expression. 当 stackalloc_initializer 的类型为时 K* ，将存在从 stackalloc_initializer 到类型的隐式 stackalloc 转换 System.Span<K> 。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>.