Using Optional Labeled Function Arguments
If you are constructing a function that takes some arguments, but one of those arguments has a reasonable default value, then you can use an optional labeled argument. Labeled arguments are those arguments prefixed with a ~
. If you give the argument a default value, then it becomes optional.
let thing = (~a=1, b: int, c: int) => {
a + b + c;
};
In this case ~a
is a labeled argument. It is also optional and will default to 1
if not specified. The other two arguments, b
and c
, are positional arguments and thus required in order for the function to evaluate.
Here are two ways of using this function either by specifying ~a
or excluding it so that it defaults to 1
.
thing(~a=2, 1, 1)
|> string_of_int
|> print_endline /* 4 */
thing(1, 1)
|> string_of_int
|> print_endline /* 3 */
See more details here.
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