www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - Compile-Time Only Function

reply Moinak Bhattacharyya <moinakb001 gmail.com> writes:
Is there an annotation that declares a function compile-time 
only? I'm attempting to use a mixin string generating function 
that uses standard druntime imports, but I'm working in a 
no-stdlib environment. I never need to use this function at 
runtime (as is the case, I imagine, with a great many of mixin 
string generating functions) so is there a way I can omit it?
Jun 23 2017
next sibling parent reply Stefan Koch <uplink.coder googlemail.com> writes:
On Friday, 23 June 2017 at 10:46:11 UTC, Moinak Bhattacharyya 
wrote:

 Is there an annotation that declares a function compile-time 
 only? I'm attempting to use a mixin string generating function 
 that uses standard druntime imports, but I'm working in a 
 no-stdlib environment. I never need to use this function at 
 runtime (as is the case, I imagine, with a great many of mixin 
 string generating functions) so is there a way I can omit it?


There is no such annotation.
However what you can do is to put your function into a function 
literal and enclose it with if (__ctfe)

which would look like this

string GenString(bla, blubb)
{
   if (__ctfe) {
     auto functionBody = () {
      // .... your body with imports and all
     }
     return functionBody(bla, blubb);
   }
   else
   {
     assert(0);
   }
}

this should hopefully keep the compile-time code out of your 
executable.
It is even more effective if you use a immediately invoked 
function literal directly inside the mixin.
which will also cause the symbol for the function to invisible 
and therefore not generated.
Jun 23 2017
parent reply Moinak Bhattacharyya <moinakb001 gmail.com> writes:
On Friday, 23 June 2017 at 10:52:25 UTC, Stefan Koch wrote:

 string GenString(bla, blubb)


That still keeps string (an associative array) as a runtime 
symbol thus requires druntime. How can I remove the string-y part?
Jun 23 2017
parent reply Moinak Bhattacharyya <moinakb001 gmail.com> writes:
On Friday, 23 June 2017 at 11:04:52 UTC, Moinak Bhattacharyya 
wrote:

 On Friday, 23 June 2017 at 10:52:25 UTC, Stefan Koch wrote:

 string GenString(bla, blubb)


 That still keeps string (an associative array) as a runtime 
 symbol thus requires druntime. How can I remove the string-y 
 part?


My mistake, it's typeinfo that's being included now. So is 
memcpy. I don't know why, as they are never used at runtime. How 
can I avoid this?
Jun 23 2017
parent reply Mike <none none.com> writes:
On Friday, 23 June 2017 at 11:24:14 UTC, Moinak Bhattacharyya 
wrote:


 My mistake, it's typeinfo that's being included now. So is 
 memcpy. I don't know why, as they are never used at runtime. 
 How can I avoid this?


Unless you're using GDC with this 
(https://github.com/D-Programming-GDC/GDC/pull/456), TypeInfo is 
always going to be included.

The only way to get a build is write TypeInfo stubs like this 
(https://github.com/JinShil/minimal_druntime_experiment/blob/master/source/d/runtime/object.d#L51)

If you're trying to use D without the runtime, you're going to 
have to provide certain implementations depending on which 
features of D you are using.

Mike
Jun 23 2017
parent reply Moinak Bhattacharyya <moinakb001 gmail.com> writes:
On Friday, 23 June 2017 at 11:29:52 UTC, Mike wrote:

 On Friday, 23 June 2017 at 11:24:14 UTC, Moinak Bhattacharyya 
 wrote:


 My mistake, it's typeinfo that's being included now. So is 
 memcpy. I don't know why, as they are never used at runtime. 
 How can I avoid this?


 Unless you're using GDC with this 
 (https://github.com/D-Programming-GDC/GDC/pull/456), TypeInfo 
 is always going to be included.

 The only way to get a build is write TypeInfo stubs like this 
 (https://github.com/JinShil/minimal_druntime_experiment/blob/master/source/d/runtime/object.d#L51)

 If you're trying to use D without the runtime, you're going to 
 have to provide certain implementations depending on which 
 features of D you are using.

 Mike


I think there should be a decoupling of the compile-time and 
runtime library. When I provide a stub object.d, the compile-time 
function fails due to missing implementations.
Jun 23 2017
parent Mike <none none.com> writes:
On Friday, 23 June 2017 at 11:50:08 UTC, Moinak Bhattacharyya 
wrote:


 I think there should be a decoupling of the compile-time and 
 runtime library. When I provide a stub object.d, the 
 compile-time function fails due to missing implementations.


Welcome to the club!
Jun 23 2017
prev sibling parent reply Mike <none none.com> writes:
On Friday, 23 June 2017 at 10:46:11 UTC, Moinak Bhattacharyya 
wrote:

 Is there an annotation that declares a function compile-time 
 only? I'm attempting to use a mixin string generating function 
 that uses standard druntime imports, but I'm working in a 
 no-stdlib environment. I never need to use this function at 
 runtime (as is the case, I imagine, with a great many of mixin 
 string generating functions) so is there a way I can omit it?


I don't know of any way to generate a compile-time error if a 
function cannot be evaluated at compile-time.  I think you will 
have to use a manifest constant 
(https://dlang.org/spec/enum.html#manifest_constants) to force 
evaluation at compile time.

// If you're not using druntime, you'll have to define the
// string type as an alias to an immutable char array.
// See 
https://github.com/dlang/druntime/blob/master/src/object.d#L41
alias immutable(char)[] string;

string GenString(string a, string b)
{
     return a ~ ", " ~ b;
}

void main()
{
     // `result` is a manifest constant that contains your
     // compile-time string, do as you wish with it
     enum result = GenString("Hello", "World");
}
Jun 23 2017
parent reply Moinak Bhattacharyya <moinakb001 gmail.com> writes:
On Friday, 23 June 2017 at 12:23:23 UTC, Mike wrote:

 alias immutable(char)[] string;

 string GenString(string a, string b)
 {
     return a ~ ", " ~ b;
 }

 void main()
 {
     // `result` is a manifest constant that contains your
     // compile-time string, do as you wish with it
     enum result = GenString("Hello", "World");
 }


The problem is, I have to concat a string with an int thus I need 
to use std.conv. This creates all sorts of problems. Do i really 
need to create my own itoa function?
Jun 23 2017
next sibling parent Stefan Koch <uplink.coder googlemail.com> writes:
On Friday, 23 June 2017 at 12:29:09 UTC, Moinak Bhattacharyya 
wrote:

 On Friday, 23 June 2017 at 12:23:23 UTC, Mike wrote:

 alias immutable(char)[] string;

 string GenString(string a, string b)
 {
     return a ~ ", " ~ b;
 }

 void main()
 {
     // `result` is a manifest constant that contains your
     // compile-time string, do as you wish with it
     enum result = GenString("Hello", "World");
 }


 The problem is, I have to concat a string with an int thus I 
 need to use std.conv. This creates all sorts of problems. Do i 
 really need to create my own itoa function?


The the one from 
https://github.com/UplinkCoder/bf-ctfe/blob/master/source/bf_compiler.d
and 
https://github.com/UplinkCoder/bf-ctfe/blob/master/source/bf_fastmath.d
Jun 23 2017
prev sibling parent Mike <none none.com> writes:
On Friday, 23 June 2017 at 12:29:09 UTC, Moinak Bhattacharyya 
wrote:


 Do i really need to create my own itoa function?


Yes, I believe you do.  I don't think the compiler has any 
built-in "to_string" evaluation.  Even the druntime authors had 
to do this 
(https://github.com/dlang/druntime/blob/1b374914ec4e28afb87186fe51ab429df52d3322/src/cor
/internal/string.d) so they wouldn't have a dependency on Phobos.

Mike
Jun 23 2017