Function Tag.expectTagValue

Lookup a child tag by name, and retrieve a value of type T from it. Throws if not found,

Useful if you only expect one value of type T from a given tag. Only looks for immediate child tags of this, doesn't search recursively.

This is a shortcut for expectTag().expectValue().

Prototype

T expectTagValue(T)(
  string fullTagName
)
if (isValueType!T);

Example

import std.exception;
import sdlang.parser;

auto root = parseSource(`
	foo 1 "a" 2 "b"
	foo 3 "c" 4 "d"  // expectTagValue considers this to override the first foo
	
	bar "hi"
	bar 379  // expectTagValue considers this to override the first bar
`);
assert( root.expectTagValue!int("foo") == 3 );
assert( root.expectTagValue!string("foo") == "c" );

// The last "bar" tag doesn't have a string (only the first "bar" tag does)
// If you'd rather receive a default value than an exception, use `getTagValue` instead.
assertThrown!ValueNotFoundException( root.expectTagValue!string("bar") );

// Tag not found
assertThrown!TagNotFoundException( root.expectTagValue!int("doesnt-exist") );

// Using namespaces:
root = parseSource(`
	ns1:foo 1 "a" 2 "b"
	ns1:foo 3 "c" 4 "d"
	ns2:foo 11 "aa" 22 "bb"
	ns2:foo 33 "cc" 44 "dd"
	
	ns1:bar "hi"
	ns1:bar 379  // expectTagValue considers this to override the first bar
`);
assert( root.expectTagValue!int("ns1:foo") == 3  );
assert( root.expectTagValue!int("*:foo"  ) == 33 ); // Search all namespaces

assert( root.expectTagValue!string("ns1:foo") == "c"  );
assert( root.expectTagValue!string("*:foo"  ) == "cc" ); // Search all namespaces

// The last "bar" tag doesn't have a string (only the first "bar" tag does)
assertThrown!ValueNotFoundException( root.expectTagValue!string("*:bar") );

// Namespace not found
assertThrown!TagNotFoundException( root.expectTagValue!int("doesnt-exist:bar") );

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