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digitalmars.D.learn - Anyone have a function to print out the field name and its value?

reply Andrej Mitrovic <none none.none> writes:
Let's say I have this structure:

struct PAINTSTRUCT
{
    bool state;
}

And somewhere in my main code I want to print out the value of state. But I
also want to know what I'm printing out. So usually I'd do this:
void main()
{
    PAINTSTRUCT ps;
    writefln("ps.state = %s", ps.state);
}

Has anyone written a function which will automatically print out both the
variable name and any object it might be part of, and then the value?

E.g. I'd like to use a function like this:
writeField(ps.state);

And if state is false it would print out to the console:
"ps.state = false"

I can't really touch PRINTSTRUCT because it's already defined as a WinAPI
structure and messing with that would be bad, so I can't implement toString()
or any helper functions within the struct. I need an outside function which
could do this automatically for any object/struct type.
Apr 09 2011
next sibling parent Andrej Mitrovic <none none.none> writes:
Andrej Mitrovic Wrote:

 



Actually I couldn't really just use "ps.fErase", because that just passes a
bool to the function. Hmm.. this doesn't look possible to do without
introducing complexity at the calling site.
Apr 09 2011
prev sibling next sibling parent reply Robert Clipsham <robert octarineparrot.com> writes:
On 09/04/2011 18:13, Andrej Mitrovic wrote:

 Let's say I have this structure:

 struct PAINTSTRUCT
 {
      bool state;
 }

 And somewhere in my main code I want to print out the value of state. But I
also want to know what I'm printing out. So usually I'd do this:
 void main()
 {
      PAINTSTRUCT ps;
      writefln("ps.state = %s", ps.state);
 }

 Has anyone written a function which will automatically print out both the
variable name and any object it might be part of, and then the value?

 E.g. I'd like to use a function like this:
 writeField(ps.state);

 And if state is false it would print out to the console:
 "ps.state = false"

 I can't really touch PRINTSTRUCT because it's already defined as a WinAPI
structure and messing with that would be bad, so I can't implement toString()
or any helper functions within the struct. I need an outside function which
could do this automatically for any object/struct type.



Off the top of my head (untested):
----
void print(T)(T t) if (is(T == struct) || is(T == class))
{
     foreach (i, field; t.tupleof)
     {
         writefln(T.tupleof[i].stringof ~ " = %s", field);
     }
}
----

--
Robert
http://octarineparrot.com/
Apr 09 2011
next sibling parent reply Robert Clipsham <robert octarineparrot.com> writes:
On 09/04/2011 18:23, Robert Clipsham wrote:

 Off the top of my head (untested):
 ----
 void print(T)(T t) if (is(T == struct) || is(T == class))
 {
 foreach (i, field; t.tupleof)
 {
 writefln(T.tupleof[i].stringof ~ " = %s", field);
 }
 }
 ----

 --
 Robert
 http://octarineparrot.com/



I forgot to mention... Usage:
---
print(myStruct);
----

It's also simple enough to adapt to just print a given field etc.

-- 
Robert
http://octarineparrot.com/
Apr 09 2011
parent Robert Clipsham <robert octarineparrot.com> writes:
On 09/04/2011 18:44, Andrej Mitrovic wrote:

 On 4/9/11, Andrej Mitrovic<andrej.mitrovich gmail.com>  wrote:

 That's great, I can use it to print out all the fields. Thanks!



 Some error checking should be done, or maybe there's a bug. If a field
 has a type that is a typedef to say a void*:
 typedef void* HANDLE

 struct S
 {
      HANDLE hnd;
 }

 Printing hnd will fail with an error:

 D:\DMD\dmd2\windows\bin\..\..\src\phobos\std\format.d(1599): Error:
 function std.format.formatValue!(LockingTextWriter,HANDLE,immutable(char)).formatValue
 is deprecated
 D:\DMD\dmd2\windows\bin\..\..\src\phobos\std\format.d(308): Error:
 template instance
 std.format.formatGeneric!(LockingTextWriter,HANDLE,immutable(char))
 error instantiating
 D:\DMD\dmd2\windows\bin\..\..\src\phobos\std\stdio.d(701):
 instantiated from here:
 formattedWrite!(LockingTextWriter,immutable(char),HANDLE)
 D:\DMD\dmd2\windows\bin\..\..\src\phobos\std\stdio.d(1598):        instantiated
 from here: writefln!(string,HANDLE)
 hello_msg.d(35):        instantiated from here: writefln!(string,HANDLE)
 hello_msg.d(129):        instantiated from here: print!(PAINTSTRUCT)



For now you can compile with -d, this should be reported as a bug though.


 Btw, why are we not allowed to have mixin templates that have
 statements? Why only declarations?



Dunno, never made sense to me... Could be a question for d.D.

--
Robert
http://octarineparrot.com/
Apr 09 2011
prev sibling next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 4/9/11, Robert Clipsham <robert octarineparrot.com> wrote:

 On 09/04/2011 18:23, Robert Clipsham wrote:

 Off the top of my head (untested):
 ----
 void print(T)(T t) if (is(T == struct) || is(T == class))
 {
 foreach (i, field; t.tupleof)
 {
 writefln(T.tupleof[i].stringof ~ " = %s", field);
 }
 }
 ----

 --
 Robert
 http://octarineparrot.com/



 I forgot to mention... Usage:
 ---
 print(myStruct);
 ----

 It's also simple enough to adapt to just print a given field etc.

 --
 Robert
 http://octarineparrot.com/



That's great, I can use it to print out all the fields. Thanks!
Apr 09 2011
prev sibling next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 4/9/11, Andrej Mitrovic <andrej.mitrovich gmail.com> wrote:

 That's great, I can use it to print out all the fields. Thanks!



Some error checking should be done, or maybe there's a bug. If a field
has a type that is a typedef to say a void*:
typedef void* HANDLE

struct S
{
    HANDLE hnd;
}

Printing hnd will fail with an error:

D:\DMD\dmd2\windows\bin\..\..\src\phobos\std\format.d(1599): Error:
function std.format.formatValue!(LockingTextWriter,HANDLE,immutable(char)).formatValue
is deprecated
D:\DMD\dmd2\windows\bin\..\..\src\phobos\std\format.d(308): Error:
template instance
std.format.formatGeneric!(LockingTextWriter,HANDLE,immutable(char))
error instantiating
D:\DMD\dmd2\windows\bin\..\..\src\phobos\std\stdio.d(701):
instantiated from here:
formattedWrite!(LockingTextWriter,immutable(char),HANDLE)
D:\DMD\dmd2\windows\bin\..\..\src\phobos\std\stdio.d(1598):        instantiated
from here: writefln!(string,HANDLE)
hello_msg.d(35):        instantiated from here: writefln!(string,HANDLE)
hello_msg.d(129):        instantiated from here: print!(PAINTSTRUCT)

Btw, why are we not allowed to have mixin templates that have
statements? Why only declarations?
Apr 09 2011
prev sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 4/9/11, Robert Clipsham <robert octarineparrot.com> wrote:

 For now you can compile with -d, this should be reported as a bug though.



Ok, reported. http://d.puremagic.com/issues/show_bug.cgi?id=5825


 Dunno, never made sense to me... Could be a question for d.D.



Yup. :)
Apr 09 2011
prev sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
Wow, I figured out a trick. Check it out, two modules:

1. fieldwrite.d:
module fieldwrite;

import std.string;
import std.stdio;
import std.conv;

mixin template field(string T)
{
    struct FieldTemp
    {
        this(string str)
        {
            writefln(str ~ " = %s", mixin(T));
        }
    }

    FieldTemp fieldTemp = FieldTemp(T);
}

2. driver.d:

import std.stdio;
import fieldwrite;

struct S
{
    int x;
    int y;
}

void main()
{
    S s;
    s.x = 1;
    s.y = 2;

    mixin field!"s.x";
    mixin field!"s.y";
}
Apr 09 2011