C# Language Specification

Local variables

A local variable is declared by a local-variable-declaration, which may occur in a block, a for-statement, a switch-statement or a using-statement; or by a foreach-statement or a specific-catch-clause for a try-statement.

The lifetime of a local variable is the portion of program execution during which storage is guaranteed to be reserved for it. This lifetime extends at least from entry into the block, for-statement, switch-statement, using-statement, foreach-statement, or specific-catch-clause with which it is associated, until execution of that block, for-statement, switch-statement, using-statement, foreach-statement, or specific-catch-clause ends in any way. (Entering an enclosed block or calling a method suspends, but does not end, execution of the current block, for-statement, switch-statement, using-statement, foreach-statement, or specific-catch-clause.) If the local variable is captured by an anonymous function (§7.15.5.1), its lifetime extends at least until the delegate or expression tree created from the anonymous function, along with any other objects that come to reference the captured variable, are eligible for garbage collection.

If the parent block, for-statement, switch-statement, using-statement, foreach-statement, or specific-catch-clause is entered recursively, a new instance of the local variable is created each time, and its local-variable-initializer, if any, is evaluated each time.

A local variable introduced by a local-variable-declaration is not automatically initialized and thus has no default value. For the purpose of definite assignment checking, a local variable introduced by a local-variable-declaration is considered initially unassigned. A local-variable-declaration may include a local-variable-initializer, in which case the variable is considered definitely assigned only after the initializing expression (§5.3.3.4).

Within the scope of a local variableintroduced by a local-variable-declaration, it is a compile-time error to refer to that local variable in a textual position that precedes its local-variable-declarator. If the local variable declaration is implicit (§8.5.1), it is also an error to refer to the variable within its local-variable-declarator.

A local variable introduced by a foreach-statement or a specific-catch-clause is considered definitely assigned in its entire scope.

The actual lifetime of a local variable is implementation-dependent. For example, a compiler might statically determine that a local variable in a block is only used for a small portion of that block. Using this analysis, the compiler could generate code that results in the variable’s storage having a shorter lifetime than its containing block.

The storage referred to by a local reference variable is reclaimed independently of the lifetime of that local reference variable (§3.9).

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