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digitalmars.D.learn - emulate with

reply Amex <Amex gmail.com> writes:
with lets one remove a direct reference...

The problem is the things I want to access are not part of a 
single object but have a common naming structure:

X_A
X_B
X_C_Q

(rather than X.A, X.B, X.C.Q)

it would be very helpful(since X is long) to be able to do 
something like

with(X)
{
     A;
     B;
     C_Q;
}

or even

with(X)
{
     A;
     B;
     with(C)
     {
         Q;
     }
}


I imagine this can actually be done with dispatching because one 
could use opDispatch to redirect. The problem is that this 
requires filling out the info which sorta defeated the 
purpose(unless it's used often).

What I'm talking about is that if A would be dispatched to, say, 
W!X where W handles the special dispatching by returning X_A 
rather than X.A.


I don't know if D can do this kinda stuff even though it would be 
rather simple as it would depend on with.

e.g., would be cool if there was an opWith ;)
May 31 2019
next sibling parent KnightMare <black80 bk.ru> writes:
imo for parts of names such things will never appear.. names, 
subnames, overloading.. hell no

but I want Kotlin lambdas
https://kotlinlang.org/docs/reference/lambdas.html
I want more:
Function literals with receiver
it: implicit name of a single parameter
Passing a lambda to the last parameter
than will appear
https://ask.ericlin.info/post/2017/06/subtle-differences-between-kotlins-with-apply-let-also-and-run/
https://medium.com/tompee/idiomatic-kotlin-lambdas-with-receiver-and-dsl-3cd3348e1235
May 31 2019
prev sibling parent reply Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:
On Friday, 31 May 2019 at 07:17:22 UTC, Amex wrote:

 What I'm talking about is that if A would be dispatched to, 
 say, W!X where W handles the special dispatching by returning 
 X_A rather than X.A.


 I don't know if D can do this kinda stuff even though it would 
 be rather simple as it would depend on with.


Of course D can! However, it's not really pretty, and I think I 
found a bug in the process.

This is my code that compiles and runs:

void X_A(int i) {}
void X_A(string s) {}
void X_B(int i) {}
void X_C_Q(int i) {}

unittest {
     with (Dispatcher.X!({})) {
         A(1);
         A("a");
         B(2);
         C_Q(3);
     }
}

template getMethod(alias x, string name) {
     static if (__traits(hasMember, x, name)) {
         alias getMethod = __traits(getMember, x, name);
     } else static if (x.stringof[0..7] == "module ") {
         import std.meta : AliasSeq;
         alias getMethod = AliasSeq!();
     } else {
         alias getMethod = getMethod!(__traits(parent, x), name);
     }
}

struct Dispatcher {
     template opDispatch(string prefix) {
         static auto opDispatch(alias context)() {
             struct WithObject {
                 auto opDispatch(string name, A...)(A a) {
                     struct OverloadCaller {
                         auto opCall(Args...)(Args args) {
                             return getMethod!(context, 
prefix~"_"~name)(args);
                         }
                     }
                     OverloadCaller result;
                     return result;
                 }
             }
             return WithObject();
         }
     }
}

So, the ugly:

1) Instead of just Dispatcher.X, we need to give Dispatcher a 
context from where to look for X_<something>. That's the curly 
brackets in Dispatcher.X!({}).

2) The bug I mentioned. The whole OverloadCaller deal is a silly 
workaround for WithObject's opDispatch not being called correctly 
by DMD. That's also why WithObject's opDispatch takes (A...)(A 
a). I'll be filing this, of course.

3) with doesn't correctly handle static opDispatch. I'll be 
filing a bug for that as well.

We could fix 1) by introducing a new magic identifier - something 
like __CONTEXT__, which would work somewhat like __FUNCTION__, 
but be useful for reflection with __traits. I've played a little 
with this idea, but I'm not ready to make a PR with it.

With 1), 2) and 3) fixed, the code would look like this (only 
changed code included):

unittest {
     with (Dispatcher.X) {
         A(1);
         A("a");
         B(2);
         C_Q(3);
     }
}

struct Dispatcher {
     struct opDispatch(string prefix, alias context = __CONTEXT__) 
{
         static auto opDispatch(string name, Args...)(Args args) {
              return getMethod!(context, prefix~"_"~name)(args);
         }
     }
}

I think that's kinda neat, TBH.

--
   Simen
May 31 2019
next sibling parent Amex <Amex gmail.com> writes:
On Friday, 31 May 2019 at 08:35:23 UTC, Simen Kjærås wrote:

 On Friday, 31 May 2019 at 07:17:22 UTC, Amex wrote:

 What I'm talking about is that if A would be dispatched to, 
 say, W!X where W handles the special dispatching by returning 
 X_A rather than X.A.


 I don't know if D can do this kinda stuff even though it would 
 be rather simple as it would depend on with.


 Of course D can! However, it's not really pretty, and I think I 
 found a bug in the process.

 This is my code that compiles and runs:

 void X_A(int i) {}
 void X_A(string s) {}
 void X_B(int i) {}
 void X_C_Q(int i) {}

 unittest {
     with (Dispatcher.X!({})) {
         A(1);
         A("a");
         B(2);
         C_Q(3);
     }
 }

 template getMethod(alias x, string name) {
     static if (__traits(hasMember, x, name)) {
         alias getMethod = __traits(getMember, x, name);
     } else static if (x.stringof[0..7] == "module ") {
         import std.meta : AliasSeq;
         alias getMethod = AliasSeq!();
     } else {
         alias getMethod = getMethod!(__traits(parent, x), name);
     }
 }

 struct Dispatcher {
     template opDispatch(string prefix) {
         static auto opDispatch(alias context)() {
             struct WithObject {
                 auto opDispatch(string name, A...)(A a) {
                     struct OverloadCaller {
                         auto opCall(Args...)(Args args) {
                             return getMethod!(context, 
 prefix~"_"~name)(args);
                         }
                     }
                     OverloadCaller result;
                     return result;
                 }
             }
             return WithObject();
         }
     }
 }

 So, the ugly:

 1) Instead of just Dispatcher.X, we need to give Dispatcher a 
 context from where to look for X_<something>. That's the curly 
 brackets in Dispatcher.X!({}).

 2) The bug I mentioned. The whole OverloadCaller deal is a 
 silly workaround for WithObject's opDispatch not being called 
 correctly by DMD. That's also why WithObject's opDispatch takes 
 (A...)(A a). I'll be filing this, of course.

 3) with doesn't correctly handle static opDispatch. I'll be 
 filing a bug for that as well.

 We could fix 1) by introducing a new magic identifier - 
 something like __CONTEXT__, which would work somewhat like 
 __FUNCTION__, but be useful for reflection with __traits. I've 
 played a little with this idea, but I'm not ready to make a PR 
 with it.

 With 1), 2) and 3) fixed, the code would look like this (only 
 changed code included):

 unittest {
     with (Dispatcher.X) {
         A(1);
         A("a");
         B(2);
         C_Q(3);
     }
 }

 struct Dispatcher {
     struct opDispatch(string prefix, alias context = 
 __CONTEXT__) {
         static auto opDispatch(string name, Args...)(Args args) 
 {
              return getMethod!(context, prefix~"_"~name)(args);
         }
     }
 }

 I think that's kinda neat, TBH.

 --
   Simen



Thanks, I haven't messed with it but it by your examples it 
should do what I want...

I actually probably need the use of .'s turned in to _'s... so I 
can write stuff like

A.B.C.D and it all goes to X.A_B_C_D.

I'm not sure if A.B.C.D would get dispatched as a whole or just 
in part though(e.g., is it treated as A.(B.(C.D)) or (A.B).C).D 
or A.B.C.D) which would require some type of chaining dispatcher 
I guess).

In any case it helps with my specific problem. I like the idea of 
_CONTEXT_ and it might be usable in other areas.

Thanks.
May 31 2019
prev sibling parent Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:
On Friday, 31 May 2019 at 08:35:23 UTC, Simen Kjærås wrote:

 With 1), 2) and 3) fixed, the code would look like this (only 
 changed code included):

 unittest {
     with (Dispatcher.X) {
         A(1);
         A("a");
         B(2);
         C_Q(3);
     }
 }

 struct Dispatcher {
     struct opDispatch(string prefix, alias context = 
 __CONTEXT__) {
         static auto opDispatch(string name, Args...)(Args args) 
 {
              return getMethod!(context, prefix~"_"~name)(args);
         }
     }
 }


Actually, Dispatcher could look like this:

struct Dispatcher {
     struct opDispatch(string prefix, alias context = __CONTEXT__) 
{
         alias opDispatch(string name) = getMethod!(context, 
prefix~"_"~name);
     }
}

--
   Simen
Jun 01 2019