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Function object.update

Calls create if key doesn't exist in the associative array, otherwise calls update. create returns a corresponding value for key. update accepts a key parameter. If it returns a value, the value is set for key.

void update(K, V, C, U) (
  ref V[K] aa,
  K key,
  scope C create,
  scope U update
)
if (is(typeof(create()) : V) && (is(typeof(update(aa[K.init])) : V) || is(typeof(update(aa[K.init])) == void)));

Parameters

NameDescription
aa The associative array.
key The key.
create The callable to create a value for key. Must return V.
update The callable to call if key exists. Takes a K argument, returns a V or void.

Example

int[string] aa;

// create
aa.update("key",
    () => 1,
    (int) {} // not executed
    );
writeln(aa["key"]); // 1

// update value by ref
aa.update("key",
    () => 0, // not executed
    (ref int v) {
        v += 1;
    });
writeln(aa["key"]); // 2

// update from return value
aa.update("key",
    () => 0, // not executed
    (int v) => v * 2
    );
writeln(aa["key"]); // 4

// 'update' without changing value
aa.update("key",
    () => 0, // not executed
    (int) {
        // do something else
    });
writeln(aa["key"]); // 4

Authors

Walter Bright, Sean Kelly

License

Boost License 1.0.