std.string phobos

[pc]

dsimcha Wrote:

> == Quote from pc (peng2cheng2 at yahoo.com)'s article
> > Is there a way to make the functions in std.string, such as replace, pure? Many
> pure functions are going to  want to use these. Also, could some of them be
> executable at compile time?
> > For me, using D2.032, this did not compile.
> > pure string replaceXX(string str){
> >   return replace(str,"XX","X");
> > }
> > If I am missing something, help!
> 
> For a function in D to pass the compiler checks for purity, it must only call
> functions that are *marked as* being pure.  If a function is not marked as pure
> but is de facto pure, it won't work.  For example:
> 
> uint nPlus2(uint n) pure {
>     return nPlus1( nPlus1( n));  // Not pure.
> }
> 
> uint nPlus1(uint n) {
>     return n + 1;
> }
> 
> Many functions that are, in fact, pure, have not been annotated as such yet in
> Phobos, since pure was implemented fairly recently.  If you want to help out, this
> is fairly low hanging fruit.
> 
> Also, purity is very restrictive right now and is designed partly with thread
> safety in mind.  A function that truly has no side effects from an observable
> behavior in a single thread point of view won't necessarily pass the compiler as pure:
> 
> __gshared uint foo;
> 
> /* wasteTime() is impure even though it has no observable side
>  * effects in a single thread because it still (at least
>  * temporarily) manipulates global state, and thus could
>  * cause problems in multithreaded code.  Furthermore, even if
>  * it were thread safe, it would be hard to prove for all but
>  * the simplest cases that functions like these have no
>  * observable side effects.*/
> void wasteTime() pure {  // Won't compile.
>    foo++;
>    foo--;
> }

Thank you for the helpful comments.

Re helping out, I would like to help, but at this stage I feel that I need to learn much much more before I can be of any use. (I am a recently retired international income tax consultant). If I get up to speed, I will certainly help.

I was thinking that it would be good if std.string was completely templated to work for char, wchar and dchar (My main hobby is learning Chinese, so I have an interest in unicode.) I also thought the functions should be pure. The first step in this direction, and to learn D2, was to write

      immutable(T)[][] csvSplit(T)(immutable(T)[], T sep=',', T quote='"');

This worked out pretty well for string, wstring and dstring. (copy attached). I take no credit for anything clever in the code (its all based on a lisp program written by Alain Picard that is availble on the web -- it was by far the easiest to understand).

Here's the catch -- I could not make csvSplit pure. The inner functions were referencing cvsSplits local variables.  I think that the problem only occurs in templates. The following isolates the issue:



import std.stdio;

/*
  ATTEMPT TO USE NESTED "PURE" FUNCTIONS IN A TEMPLATE.

  All works fine unless you uncomment the third line in main. If you
  do, dmd 2.032 yeilds:

  pure.d(35): Error: pure nested function 'bar' cannot access mutable
  data 'fooState'

  pure.d(36): Error: pure nested function 'bar' cannot access mutable
  data 'y'

  pure.d(47): Error: template instance pure.fooPT!(char) error
  instantiating
*/


//"pure" inner function, with concrete types - ok
pure string foo(string x, string y){
  
  string fooState;

  string bar(string x){
    fooState = "hello ";
    return x ~ y;
  }

  return fooState ~ bar(x);
}

//potentially pure (?) templated version not labled as pure - ok
immutable(T)[] fooT(T)(immutable(T)[] x, immutable(T)[] y){

  immutable(T)[] fooState;

  immutable(T)[] bar(immutable(T)[] x){
    fooState = "hello ";
    return x ~ y;
  }

  return fooState ~ bar(x);

}

//attempt to make templated version pure - no dice
pure immutable(T)[] fooPT(T)(immutable(T)[] x, immutable(T)[] y){

  immutable(T)[] fooState;

  immutable(T)[] bar(immutable(T)[] x){
    fooState = "hello ";
    return x ~ y;
  }

  return fooState ~ bar(x);

}


void main(){
  writeln(foo("p", "c"));
  writeln(fooT("p", "c"));
  //writeln(fooPT("p", "c"));

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