Template std.variant.visit

The delegate or function having the currently held value as parameter is called with variant's current value. Visiting handlers are passed in the template parameter list. It is statically ensured that all types of variant are handled across all handlers. visit allows delegates and static functions to be passed as parameters.

If a function without parameters is specified, this function is called when variant doesn't hold a value. Exactly one parameter-less function is allowed.

Duplicate overloads matching the same type in one of the visitors are disallowed.

Arguments

template visit(Handler...);

Functions

Returns

The return type of visit is deduced from the visiting functions and must be the same across all overloads.

Throws

If no parameter-less, error function is specified: VariantException if variant doesn't hold a value.

Example

Algebraic!(int, string) variant;

variant = 10;
assert(variant.visit!((string s) => cast(int)s.length,
                      (int i)    => i)()
                      == 10);
variant = "string";
assert(variant.visit!((int i) => i,
                      (string s) => cast(int)s.length)()
                      == 6);

// Error function usage
Algebraic!(int, string) emptyVar;
auto rslt = emptyVar.visit!((string s) => cast(int)s.length,
                      (int i)    => i,
                      () => -1)();
assert(rslt == -1);