On Tuesday, 14 October 2014 at 03:34:06 UTC, Ary Borenszweig
wrote:
One simple thing we did in Crystal is to allow invoking a
function with named arguments only for arguments that have a
default value. For example:
void foo(int x, int y = 2, int z = 3) { ... }
foo(x, y: 10);
foo(x, y: 10, z: 20);
foo(x, z: 30)
But not this:
foo(x: 10)
The logic behind this is that named arguments are usually
wanted when you want to replace one of the default values while
keeping the others' defaults. You could specify names for
arguments that don't have a default value, but that only gives
a small readability aid. Changing a default value in the middle
is a new feature.
This greatly simplifies the logic, since parameter reordering
can only happen for names that have default values and you can
always fill the gaps. Also, default values can also appear last
in a function signature.
Another thought I had is that an alternative could be to have
some special syntax to say "use the default for this parameter."
I do not have experience implementing languages so perhaps I am
wrong, but it seems like it should be possible for the compiler
to get the default value and replace some placeholder with it.
Something like:
void foo(int a = 42, int b = 0){}
foo(@default, 7); //rewritten to foo(42, 7);
