Using lazily ?

[bioinfornatics]

dear,
Noob question for know if D provide a shorter way i explain
we have a struct S:

struct S{
string member1;
string member2;
string member3;
}

we parse a file:
File f = File("a path", "r");
S s;
sise_t tokenLength = "member1".length;
foreach( char[] line; f.byLine() )
mixin("s." ~ line[0 .. tokenLength] ~ " = " ~ line[tokenLength ..
$]" ); // do not work because lien is not kno at compile time


I know this do not works i.e comment but it will save some line by
checking if is member1 2 or 3

They are a shorter way to do this use lazy ?

Re: Using lazily ?

[Timon Gehr]

On 03/01/2012 10:50 PM, bioinfornatics wrote:

dear,
Noob question for know if D provide a shorter way i explain
we have a struct S:

struct S{
string member1;
string member2;
string member3;
}

we parse a file:
File f = File("a path", "r");
S s;
sise_t tokenLength = "member1".length;
foreach( char[] line; f.byLine() )
 mixin("s." ~ line[0 .. tokenLength] ~ " = " ~ line[tokenLength ..
$]" ); // do not work because lien is not kno at compile time


I know this do not works i.e comment but it will save some line by
checking if is member1 2 or 3

They are a shorter way to do this use lazy ?



struct S{
string member1;
string member2;
string member3;
}

S s;
size_t tokenLength = "member1".length;
void main(){
foreach(char[] line; stdin.byLine()) foreach(m;__traits(allMembers,S)){
if(line[0..tokenLength] == m) mixin("s."~m) = line[tokenLength 
.. $].idup;

}
}

Re: Using lazily ?

[bioinfornatics]

Le jeudi 01 mars 2012 à 23:10 +0100, Timon Gehr a écrit :
> S s;
> size_t tokenLength = "member1".length;
> void main(){
>  foreach(char[] line; stdin.byLine())
> foreach(m;__traits(allMembers,S)){
>  if(line[0..tokenLength] == m) mixin("s."~m) =
> line[tokenLength 
> .. $].idup;
>  }
> } 

awesome :)

can use hasMember instead allMembers ?

Re: Using lazily ?

[Ali Çehreli]

On 03/01/2012 02:25 PM, bioinfornatics wrote:
> Le jeudi 01 mars 2012 à 23:10 +0100, Timon Gehr a écrit :
>> S s;
>> size_t tokenLength = "member1".length;
>> void main(){
>>   foreach(char[] line; stdin.byLine())
>> foreach(m;__traits(allMembers,S)){
>>   if(line[0..tokenLength] == m) mixin("s."~m) =
>> line[tokenLength
>> .. $].idup;
>>   }
>> }
>
> awesome :)
>
> can use hasMember instead allMembers ?

No, because both of those are compile-time features. Even if you used 
hasMember, the answer will always be true:


if (__traits(hasMember, S, "member1"))

Yes, S has member1.

Note that Timon's inner foreach is a compile-time foreach, which is the 
equivalent of the following three lines:


if(line[0..tokenLength] == "member1") s.member1 = line[tokenLength .. 
$].idup;
if(line[0..tokenLength] == "member2") s.member2 = line[tokenLength .. 
$].idup;
if(line[0..tokenLength] == "member3") s.member3 = line[tokenLength .. 
$].idup;


There is no inner foreach looop that is executed at runtime.

Ali

Re: Using lazily ?

[bearophile]

Ali:

> Note that Timon's inner foreach is a compile-time foreach, which is the 
> equivalent of the following three lines:

I'd like it to be written:
static foreach (...) {...

In the meantime an annotation helps clarify the code for the person that will 
read the code:
/*static*/ foreach (...) {...

Bye,
bearophile

Re: Using lazily ?

[Timon Gehr]

On 03/02/2012 12:12 AM, bearophile wrote:

Ali:


Note that Timon's inner foreach is a compile-time foreach, which is the
equivalent of the following three lines:


I'd like it to be written:
static foreach (...) {...

In the meantime an annotation helps clarify the code for the person that will 
read the code:
/*static*/ foreach (...) {...

Bye,
bearophile


static foreach should also be available for declarations. I have a lot 
of code of the following form:


mixin({
string r;
foreach(x; [".","..","..."]) r~=X!q{...};
return r;
}());