Re: Obtaining argument names in (variadic) functions
On Thursday, 17 March 2016 at 14:12:38 UTC, Edwin van Leeuwen
wrote:
On Thursday, 17 March 2016 at 13:53:00 UTC, JR wrote:
Interesting, any idea if it is possible to do assignment
within template.. Either:
printVars!(int abc=5,string def="58")();
or something like
printVars!("abc","def",ghi)(5,"58");
What would the use-cases for those be?
I don't think the first is valid grammar, and I'm not sure
what you want the second to do. Resolve symbols by string
literals of their names? That might need a string mixin as
they wouldn't be in scope when in the called template
function, but I've never tried it.
Both use cases are when you want a named parameter, without
having to assign it first. I know the first is not valid
grammar, was just wondering if you might be smarter than me and
see a way to make it valid :)
Second one is another possible alternative that I have been
thinking about.
Basically, say I want to have the named (optional) parameters x
and y. In your initial example I would be required to do:
```
int x = 1;
string y = "2";
doSomethingWithNamedPars!(x,y)();
```
I just hoped to shorten that to a one liner similar to:
```
doSomethingWithNamedPars!(x=1,y="2")();
```
or alternatively
```
doSomethingWithNamedPars!("x","y")(1,"2");
```
(where doSomethingWithNamedPars's behaviour depends on which
named parameters it is passed)
Just as a reference, my current approach (in ggplotd) is with
named tuples, but that is slightly more verbose than I had
hoped:
```
doSomethingWithNamedPars( Tuple!(int, "x", string, "y")( 1, 2 )
);
```
http://dpaste.dzfl.pl/1625122e4f01 is the best I can do, and it's
ugly. It's something akin to your
doSomethingWithNamedPars!("x","y")(1,"2"). I may even have missed
the point.
It *neccessitates* that the called function knows the parameter
names, because they're not self-documented in the signature. It
will also have to deal with any missing ones to actually compile.
I'm not sure how to do this and still enjoy things like const and
ref and friends.
I imagine there *might* be a way to do this with normal
non-templated functions given a similar wrapper, if the functions
are annotated so that it can get the names of the parameters. It
feels like you should be able to get it to naïvely reorder the
arguments, default-initialise any missing ones, etc. But you
quickly run into "xyz cannot be read at compile-time", even when
it feels like everything should be known.
Re: Obtaining argument names in (variadic) functions
On Wednesday, 16 March 2016 at 21:05:43 UTC, JR wrote: On Wednesday, 16 March 2016 at 20:43:09 UTC, jkpl wrote: I try to anticipate the reason why you want this. [...] I use something *kinda* sort of similar in my toy project to print all fields of a struct, for debugging purposes when stuff goes wrong. Getting the names of the member variables is crucial then. http://dpaste.dzfl.pl/748c4dd97de6 That's a nice learning piece. I think "with" is cool, reminds me of a nice R feature.
Re: Obtaining argument names in (variadic) functions
On Thursday, 17 March 2016 at 11:52:13 UTC, Edwin van Leeuwen
wrote:
On Wednesday, 16 March 2016 at 20:53:42 UTC, JR wrote:
void printVars(Args...)()
if (Args.length > 0)
{
import std.stdio : writefln;
foreach (i, arg; Args) {
writefln("%s\t%s:\t%s", typeof(Args[i]).stringof,
Args[i].stringof, arg);
}
}
void main() {
int abc = 3;
string def = "58";
float ghi = 3.14f;
double jkl = 3.14;
printVars!(abc,def,ghi,jkl)();
}
Interesting, any idea if it is possible to do assignment within
template.. Either:
printVars!(int abc=5,string def="58")();
or something like
printVars!("abc","def",ghi)(5,"58");
What would the use-cases for those be?
I don't think the first is valid grammar, and I'm not sure what
you want the second to do. Resolve symbols by string literals of
their names? That might need a string mixin as they wouldn't be
in scope when in the called template function, but I've never
tried it.
You *can* cook up something that modifies the values of variables
you pass in -- like modifyVars!(abc,def,ghi)("asdf", 123, 3.14)
-- but you just might be better off with runtime ref parameters
then.
Re: Obtaining argument names in (variadic) functions
On 3/16/16 4:24 PM, data pulverizer wrote:
Hi D gurus,
is there a way to obtain parameter names within the function body? I am
particularly interested in variadic functions. Something like:
void myfun(T...)(T x){
foreach(i, arg; x)
writeln(i, " : ", arg);
}
void main(){
myfun(a = 2, b = "two", c = 2.0);
}
This isn't valid code. The name of the parameters is x[0], x[1], and x[2].
You could do something like:
myfun("a", 2, "b", "two", "c", 2.0);
and process it properly.
-Steve
Re: Obtaining argument names in (variadic) functions
On Wednesday, 16 March 2016 at 20:24:38 UTC, data pulverizer
wrote:
Hi D gurus,
is there a way to obtain parameter names within the function
body? I am particularly interested in variadic functions.
Something like:
void myfun(T...)(T x){
foreach(i, arg; x)
writeln(i, " : ", arg);
}
void main(){
myfun(a = 2, b = "two", c = 2.0);
}
// should print
a : 2
b : two
c : 2.0
Thanks in advance
Loving the mixins and tuples
You can do it precisely like that if the variables/symbols you
pass as (template) arguments are properly declared first.
http://dpaste.dzfl.pl/0b452efeaaab
void printVars(Args...)()
if (Args.length > 0)
{
import std.stdio : writefln;
foreach (i, arg; Args) {
writefln("%s\t%s:\t%s", typeof(Args[i]).stringof,
Args[i].stringof, arg);
}
}
void main() {
int abc = 3;
string def = "58";
float ghi = 3.14f;
double jkl = 3.14;
printVars!(abc,def,ghi,jkl)();
}
Obtaining argument names in (variadic) functions
Hi D gurus,
is there a way to obtain parameter names within the function
body? I am particularly interested in variadic functions.
Something like:
void myfun(T...)(T x){
foreach(i, arg; x)
writeln(i, " : ", arg);
}
void main(){
myfun(a = 2, b = "two", c = 2.0);
}
// should print
a : 2
b : two
c : 2.0
Thanks in advance
Loving the mixins and tuples
Re: Obtaining argument names in (variadic) functions
On Wednesday, 16 March 2016 at 20:53:42 UTC, JR wrote:
void printVars(Args...)()
if (Args.length > 0)
{
import std.stdio : writefln;
foreach (i, arg; Args) {
writefln("%s\t%s:\t%s", typeof(Args[i]).stringof,
Args[i].stringof, arg);
}
}
void main() {
int abc = 3;
string def = "58";
float ghi = 3.14f;
double jkl = 3.14;
printVars!(abc,def,ghi,jkl)();
}
Interesting, any idea if it is possible to do assignment within
template.. Either:
printVars!(int abc=5,string def="58")();
or something like
printVars!("abc","def",ghi)(5,"58");
Re: Obtaining argument names in (variadic) functions
On Wednesday, 16 March 2016 at 20:24:38 UTC, data pulverizer
wrote:
Hi D gurus,
is there a way to obtain parameter names within the function
body? I am particularly interested in variadic functions.
Something like:
void myfun(T...)(T x){
foreach(i, arg; x)
writeln(i, " : ", arg);
}
void main(){
myfun(a = 2, b = "two", c = 2.0);
}
// should print
a : 2
b : two
c : 2.0
Thanks in advance
Loving the mixins and tuples
I try to anticipate the reason why you want this. As said in a
previous answer you can access to an individual element by using
the array syntax but also _param_, with X the index of the
parameter:
void myfun(T...)(T x)
{
import std.traits; import std.stdio;
writeln(ParameterIdentifierTuple!(myfun!T));
writeln(_param_0);
writeln(_param_1);
writeln(_param_2);
}
void main()
{
int a=1,b=2,c=3;
myfun(a,b,c);
}
Re: Obtaining argument names in (variadic) functions
On Wednesday, 16 March 2016 at 20:53:42 UTC, JR wrote:
On Wednesday, 16 March 2016 at 20:24:38 UTC, data pulverizer
wrote:
Hi D gurus,
is there a way to obtain parameter names within the function
body? I am particularly interested in variadic functions.
Something like:
void myfun(T...)(T x){
foreach(i, arg; x)
writeln(i, " : ", arg);
}
void main(){
myfun(a = 2, b = "two", c = 2.0);
}
// should print
a : 2
b : two
c : 2.0
Thanks in advance
Loving the mixins and tuples
You can do it precisely like that if the variables/symbols you
pass as (template) arguments are properly declared first.
http://dpaste.dzfl.pl/0b452efeaaab
void printVars(Args...)()
if (Args.length > 0)
{
import std.stdio : writefln;
foreach (i, arg; Args) {
writefln("%s\t%s:\t%s", typeof(Args[i]).stringof,
Args[i].stringof, arg);
}
}
void main() {
int abc = 3;
string def = "58";
float ghi = 3.14f;
double jkl = 3.14;
printVars!(abc,def,ghi,jkl)();
}
That's brilliant! Thanks JR
Re: Obtaining argument names in (variadic) functions
On Thursday, 17 March 2016 at 13:53:00 UTC, JR wrote:
Interesting, any idea if it is possible to do assignment
within template.. Either:
printVars!(int abc=5,string def="58")();
or something like
printVars!("abc","def",ghi)(5,"58");
What would the use-cases for those be?
I don't think the first is valid grammar, and I'm not sure what
you want the second to do. Resolve symbols by string literals
of their names? That might need a string mixin as they wouldn't
be in scope when in the called template function, but I've
never tried it.
Both use cases are when you want a named parameter, without
having to assign it first. I know the first is not valid grammar,
was just wondering if you might be smarter than me and see a way
to make it valid :)
Second one is another possible alternative that I have been
thinking about.
Basically, say I want to have the named (optional) parameters x
and y. In your initial example I would be required to do:
```
int x = 1;
string y = "2";
doSomethingWithNamedPars!(x,y)();
```
I just hoped to shorten that to a one liner similar to:
```
doSomethingWithNamedPars!(x=1,y="2")();
```
or alternatively
```
doSomethingWithNamedPars!("x","y")(1,"2");
```
(where doSomethingWithNamedPars's behaviour depends on which
named parameters it is passed)
Just as a reference, my current approach (in ggplotd) is with
named tuples, but that is slightly more verbose than I had hoped:
```
doSomethingWithNamedPars( Tuple!(int, "x", string, "y")( 1, 2 ) );
```
Re: Obtaining argument names in (variadic) functions
On Wednesday, 16 March 2016 at 20:43:09 UTC, jkpl wrote: I try to anticipate the reason why you want this. [...] I use something *kinda* sort of similar in my toy project to print all fields of a struct, for debugging purposes when stuff goes wrong. Getting the names of the member variables is crucial then. http://dpaste.dzfl.pl/748c4dd97de6
