This is an idea I've been thinking of for a while, it's not a really
suggestion (at least not yet) I just wanted to here what people think
about it.
If we take a step back and look at what string mixins actually do or
rather what they're used for, that would be: inserting a piece/block of
code where the mixin expression is used. If we then take a look at how a
block of code is represented in D (how you store it in variables and how
you pass it around). It's not as a string which is used by the mixin
expression, instead delegates are used to represent a block of code in D
that can be passed around. Therefore this is my idea:
Add a new mixin operator "@" (1). When that operator is put in front of
a function call it would behave as a string mixin. The function that is
called needs to be CTFE and return a delegate or an array of delegates:
class Foo
{
@get_set("int", "bar");
}
The above code would be the same as the following code:
class Foo
{
mixin(get_set("int", "bar"));
}
If we now move to the declaration of "get_set" this is how it could look
like:
void delegate () get_set (string type, string name)
{
return
{
@type _...@name;
@type @name ()
{
return _...@name;
}
@type @name (@type @name)
{
return _...@name = @name;
}
};
}
In the above code when "@" is used in the delegate literal it basically
behaves like string interpolation, so "@type" would be replaced with the
content of the "type" variable (2).
When the "get_set" function is called with the mixin symbol the content
of the returned delegate is inserted where the call is made. If the
function returns an array of delegates then the array would be unfolded
and the content of all the delegates would be inserted.
Taking it one step further:
Allow the mixin syntax to be placed in front of most of the declarations
and drop the need for string literals, commas and parentheses, basically
allowing the following syntax:
class Foo
{
@get_set int bar;
}
Would be translated into this:
class Foo
{
@get_set!(int)("bar");
}
Maybe one could do something like this as well:
@singleton class Foo
{
}
void delegate () singleton (string name, void delegate () classBody)
{
return { // a simple singleton implementation
class @name
{
static @name instance;
static this ()
{
instance = new @name;
}
private this () {}
@classBody;
}
};
}
Above, in the last example, @classBody would insert the content of the
delegate, basically the class body.
1. I will use "@" in this example because I think it looks good but it
would probably conflict with @nothrow, @property and others.
2. I have no idea if this usage of the mixin symbol, "@", will conflict
with the first usage.
--
/Jacob Carlborg
