Difference between revisions of "Using string mixins for logging"

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{{Cookbook
 +
|category=Meta Programming
 +
|level=Novice
 +
|type=Recipe
 +
|status=Deprecated
 +
|time=10 min
 +
|dversion=D2
 +
|display=none
 +
}}
 +
 +
'''This code manually defines __FUNCTION__ which break as of D 2.063 and uses a few now obsolete workarounds. To view more up-to-date examples visit [[Logging mechanisms]]'''
 +
 +
 +
----
 +
 +
 +
This recipe uses string mixins for implementing a logging facility.
 +
The program code is given in the next section. [http://dpaste.dzfl.pl/cdacef45 ▶ Try it online]
 +
 +
==Program Code==
 
<syntaxhighlight lang="D">
 
<syntaxhighlight lang="D">
 
import std.traits : PTT=ParameterTypeTuple;
 
import std.traits : PTT=ParameterTypeTuple;
Line 38: Line 58:
 
template log(string level, PS...)
 
template log(string level, PS...)
 
{
 
{
     //pragma(msg, info);
+
     //pragma(msg, log);
     const char[] log = `static if(!__traits(compiles, __FUNCTION__ == ""))` ~  
+
     enum log = `static if(!__traits(compiles, __FUNCTION__ == ""))` ~  
                       `{ immutable string __FUNCTION__ = __traits(identifier, __traits(parent, {})) ~` ~
+
                       `{ enum __FUNCTION__ = __traits(identifier, __traits(parent, {})) ~` ~
                                                        `"(" ~ StringOf!(PTT!(__traits(parent, {}))) ~ ")";` ~
+
                                            `"(" ~ StringOf!(PTT!(__traits(parent, {}))) ~ ")";` ~
 
                       `} stderr.writeln(Clock.currTime(), " [` ~ level ~ `] ", __FILE__, '(', __LINE__, "): ",` ~
 
                       `} stderr.writeln(Clock.currTime(), " [` ~ level ~ `] ", __FILE__, '(', __LINE__, "): ",` ~
 
                                         `__FUNCTION__, ": ",` ~ ArgStringOf!(PS) ~ `);` ;
 
                                         `__FUNCTION__, ": ",` ~ ArgStringOf!(PS) ~ `);` ;
 
}
 
}
 
+
 
template info(PS...)
 
template info(PS...)
 
{
 
{
     const char[] info = log!("INFO", PS);
+
     enum info = log!("INFO", PS);  
 
}
 
}
 
+
 
template warn(PS...)
 
template warn(PS...)
 
{
 
{
     const char[] warn = log!("WARN", PS);
+
     enum warn = log!("WARN", PS);      
 
}
 
}
 
+
 
template error(PS...)
 
template error(PS...)
 
{
 
{
     const char[] error = log!("ERROR", PS);
+
     enum error = log!("ERROR", PS);      
 
}
 
}
 
+
 
mixin template set_func_name(string fn)
 
mixin template set_func_name(string fn)
{
+
{  
     immutable string __FUNCTION__ = fn;
+
     enum __FUNCTION__ = fn;
 
}
 
}
 
+
 
/////////////////////////////////////////////////////////////////////////////////////////////////////////
 
/////////////////////////////////////////////////////////////////////////////////////////////////////////
 
+
 
import std.exception;
 
import std.exception;
 
+
 
auto foo(T)(in T val)
 
auto foo(T)(in T val)
 
     if(is(T==int) || is(T==string))
 
     if(is(T==int) || is(T==string))
Line 75: Line 95:
 
     mixin set_func_name!("foo(" ~ T.stringof ~ ")"); //workaround for fwd ref issue
 
     mixin set_func_name!("foo(" ~ T.stringof ~ ")"); //workaround for fwd ref issue
 
     mixin (info!(`"starting"`));
 
     mixin (info!(`"starting"`));
     mixin (info!(`"stopping"`));
+
 +
     scope(exit) { mixin (info!(`"stopping"`)); }
 
   
 
   
 
     static if (is(T==int))
 
     static if (is(T==int))
Line 82: Line 103:
 
         return true;
 
         return true;
 
     else
 
     else
         static assert(false, "need int or string");
+
         static assert(false, "need int or string");  
 
}
 
}
 
+
 
void baz()
 
void baz()
 
{
 
{
     mixin (info!(`"called"`));
+
     mixin (info!(`"starting"`));
+
     throw new Exception("baz");
+
    scope(exit) { mixin (info!(`"stopping"`)); }
 +
    scope(failure) { mixin (warn!(`"exception encountered"`)); }
 +
 +
     throw new Exception("bazzzz");
 
}
 
}
 
+
 
void main(string[] args)
 
void main(string[] args)
 
{
 
{
 
     mixin (info!(`"starting"`));
 
     mixin (info!(`"starting"`));
 +
 +
    scope(exit) { mixin (info!(`"stopping"`)); }
 
   
 
   
 
     mixin (info!(`"foo(1) returned: "`, `foo(1)`));
 
     mixin (info!(`"foo(1) returned: "`, `foo(1)`));
 
     mixin (info!(`"foo(\"bar\") returned: "`, `foo("bar")`));
 
     mixin (info!(`"foo(\"bar\") returned: "`, `foo("bar")`));
     mixin (warn!(`"calling baz()"`));
+
     mixin (info!(`"calling baz()"`));
 
     try
 
     try
 
     {
 
     {
Line 106: Line 132:
 
     {
 
     {
 
         mixin (error!(`"Caught exception: "`, `e.toString()`));
 
         mixin (error!(`"Caught exception: "`, `e.toString()`));
     }
+
     }  
    mixin (info!(`"stopping"`));
 
 
}
 
}
 
</syntaxhighlight>
 
</syntaxhighlight>
 
[http://dpaste.dzfl.pl/857a5f06 &#9654; Run code]
 
  
 
==Sample Output==
 
==Sample Output==
 
<pre>
 
<pre>
2012-Dec-13 21:09:13.4739137 [INFO] /home/c222/c817.d(95): main(string[]): starting
+
2012-Dec-14 19:12:58.5092108 [INFO] /home/c706/c392.d(99): main(string[]): starting
2012-Dec-13 21:09:13.4741135 [INFO] /home/c222/c817.d(75): foo(int): starting
+
2012-Dec-14 19:12:58.5093317 [INFO] /home/c706/c392.d(75): foo(int): starting
2012-Dec-13 21:09:13.4741472 [INFO] /home/c222/c817.d(76): foo(int): stopping
+
2012-Dec-14 19:12:58.5094113 [INFO] /home/c706/c392.d(77): foo(int): stopping
2012-Dec-13 21:09:13.4741115 [INFO] /home/c222/c817.d(97): main(string[]): foo(1) returned: 1.0123
+
2012-Dec-14 19:12:58.5093314 [INFO] /home/c706/c392.d(103): main(string[]): foo(1) returned: 1.0123
2012-Dec-13 21:09:13.4742436 [INFO] /home/c222/c817.d(75): foo(string): starting
+
2012-Dec-14 19:12:58.509528 [INFO] /home/c706/c392.d(75): foo(string): starting
2012-Dec-13 21:09:13.4742707 [INFO] /home/c222/c817.d(76): foo(string): stopping
+
2012-Dec-14 19:12:58.5095605 [INFO] /home/c706/c392.d(77): foo(string): stopping
2012-Dec-13 21:09:13.4742431 [INFO] /home/c222/c817.d(98): main(string[]): foo("bar") returned: true
+
2012-Dec-14 19:12:58.5095276 [INFO] /home/c706/c392.d(104): main(string[]): foo("bar") returned: true
2012-Dec-13 21:09:13.4743165 [WARN] /home/c222/c817.d(99): main(string[]): calling baz()
+
2012-Dec-14 19:12:58.5096157 [INFO] /home/c706/c392.d(105): main(string[]): calling baz()
2012-Dec-13 21:09:13.4743386 [INFO] /home/c222/c817.d(88): baz(): called
+
2012-Dec-14 19:12:58.5096436 [INFO] /home/c706/c392.d(89): baz(): starting
2012-Dec-13 21:09:13.4743744 [ERROR] /home/c222/c817.d(106): main(string[]): Caught exception: object.Exception@/home/c222/c817.d(90): baz
+
2012-Dec-14 19:12:58.5096851 [WARN] /home/c706/c392.d(92): baz(): exception encountered
 +
2012-Dec-14 19:12:58.5097154 [INFO] /home/c706/c392.d(91): baz(): stopping
 +
2012-Dec-14 19:12:58.5097433 [ERROR] /home/c706/c392.d(112): main(string[]): Caught exception: object.Exception@/home/c706/c392.d(94): bazzzz
 
----------------
 
----------------
2012-Dec-13 21:09:13.4744075 [INFO] /home/c222/c817.d(108): main(string[]): stopping
+
2012-Dec-14 19:12:58.5097807 [INFO] /home/c706/c392.d(101): main(string[]): stopping
 
</pre>
 
</pre>

Latest revision as of 11:55, 16 July 2020

Level: Novice
Cookbook Type: Recipe
Cookbook Status: Deprecated
Approximate reading time: 10 min
0.166 hr
D Version: D2


This code manually defines __FUNCTION__ which break as of D 2.063 and uses a few now obsolete workarounds. To view more up-to-date examples visit Logging mechanisms




This recipe uses string mixins for implementing a logging facility. The program code is given in the next section. ▶ Try it online

Program Code

import std.traits : PTT=ParameterTypeTuple;
import std.stdio : stderr;
import std.datetime : Clock;
 
template StringOf(TS...)
{
    static if(TS.length == 0)
    {
        enum StringOf = "";
    }
    else static if(TS.length == 1)
    {
        enum StringOf = (TS[0]).stringof;
    }
    else
    {
        enum StringOf = (TS[0]).stringof ~ "," ~ StringOf!(TS[1..$]) ;
    }
}
 
template ArgStringOf(TS...)
{
    static if(TS.length == 0)
    {
        enum ArgStringOf = "";
    }
    else static if(TS.length == 1)
    {
        enum ArgStringOf = TS[0];
    }
    else
    {
        enum ArgStringOf = TS[0] ~ "," ~ ArgStringOf!(TS[1..$]);
    }
}
 
template log(string level, PS...)
{
    //pragma(msg, log);
    enum log = `static if(!__traits(compiles, __FUNCTION__ == ""))` ~ 
                       `{ enum __FUNCTION__ = __traits(identifier, __traits(parent, {})) ~` ~
                                             `"(" ~ StringOf!(PTT!(__traits(parent, {}))) ~ ")";` ~
                       `} stderr.writeln(Clock.currTime(), " [` ~ level ~ `] ", __FILE__, '(', __LINE__, "): ",` ~
                                         `__FUNCTION__, ": ",` ~ ArgStringOf!(PS) ~ `);` ;
}
 
template info(PS...)
{
    enum info = log!("INFO", PS);    
}
 
template warn(PS...)
{
    enum warn = log!("WARN", PS);        
}
 
template error(PS...)
{
    enum error = log!("ERROR", PS);        
}
 
mixin template set_func_name(string fn)
{    
    enum __FUNCTION__ = fn;
}
 
/////////////////////////////////////////////////////////////////////////////////////////////////////////
 
import std.exception;
 
auto foo(T)(in T val)
    if(is(T==int) || is(T==string))
{
    mixin set_func_name!("foo(" ~ T.stringof ~ ")"); //workaround for fwd ref issue
    mixin (info!(`"starting"`));
 
    scope(exit) { mixin (info!(`"stopping"`)); }
 
    static if (is(T==int))
        return 1.0123;
    else static if(is(T==string))
        return true;
    else
        static assert(false, "need int or string");    
}
 
void baz()
{
    mixin (info!(`"starting"`));
 
    scope(exit) { mixin (info!(`"stopping"`)); }
    scope(failure) { mixin (warn!(`"exception encountered"`)); }
 
    throw new Exception("bazzzz");
}
 
void main(string[] args)
{
    mixin (info!(`"starting"`));
 
    scope(exit) { mixin (info!(`"stopping"`)); }
 
    mixin (info!(`"foo(1) returned: "`, `foo(1)`));
    mixin (info!(`"foo(\"bar\") returned: "`, `foo("bar")`));
    mixin (info!(`"calling baz()"`));
    try
    {
        baz();
    }
    catch(Exception e)
    {
        mixin (error!(`"Caught exception: "`, `e.toString()`));
    }    
}

Sample Output

2012-Dec-14 19:12:58.5092108 [INFO] /home/c706/c392.d(99): main(string[]): starting
2012-Dec-14 19:12:58.5093317 [INFO] /home/c706/c392.d(75): foo(int): starting
2012-Dec-14 19:12:58.5094113 [INFO] /home/c706/c392.d(77): foo(int): stopping
2012-Dec-14 19:12:58.5093314 [INFO] /home/c706/c392.d(103): main(string[]): foo(1) returned: 1.0123
2012-Dec-14 19:12:58.509528 [INFO] /home/c706/c392.d(75): foo(string): starting
2012-Dec-14 19:12:58.5095605 [INFO] /home/c706/c392.d(77): foo(string): stopping
2012-Dec-14 19:12:58.5095276 [INFO] /home/c706/c392.d(104): main(string[]): foo("bar") returned: true
2012-Dec-14 19:12:58.5096157 [INFO] /home/c706/c392.d(105): main(string[]): calling baz()
2012-Dec-14 19:12:58.5096436 [INFO] /home/c706/c392.d(89): baz(): starting
2012-Dec-14 19:12:58.5096851 [WARN] /home/c706/c392.d(92): baz(): exception encountered
2012-Dec-14 19:12:58.5097154 [INFO] /home/c706/c392.d(91): baz(): stopping
2012-Dec-14 19:12:58.5097433 [ERROR] /home/c706/c392.d(112): main(string[]): Caught exception: object.Exception@/home/c706/c392.d(94): bazzzz
----------------
2012-Dec-14 19:12:58.5097807 [INFO] /home/c706/c392.d(101): main(string[]): stopping