C# Language Specification

The CallerFilePath attribute

The System.Runtime.CompilerServices.CallerFilePathAttribute is allowed on optional parameters when there is a standard implicit conversion (§6.3.1) from string to the parameter’s type.

If a function invocation from a location in source code omits an optional parameter with the CallerFilePathAttribute, then a string literal representing that location's file path is used as an argument to the invocation instead of the default parameter value.

The format of the file path is implementation-dependent.

Note that the file path may be affected by #line directives (§2.5.7).

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