C# Language Specification

The CallerLineNumber attribute

The System.Runtime.CompilerServices.CallerLineNumberAttribute is allowed on optional parameters when there is a standard implicit conversion (§6.3.1) from the constant value int.MaxValue to the parameter’s type. This ensures that any non-negative line number up to that value can be passed without error.

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

If the invocation spans multiple lines, the line chosen is implementation-dependent.

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

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