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digitalmars.D.learn - Contract programming

reply "Oleg" <code.viator gmail.com> writes:
Is this behavior normal or it's bug?

[code]

import std.stdio;

class A
{
     float func( float x )
     in
     {
         assert( x > 0 );
         stderr.writeln( "A.func in block" );
     }
     body
     {
         stderr.writeln( "A.func body block" );
         return x / 3;
     }
}

class B : A
{
     override float func( float x )
     in
     {
         assert( x < 10 );
         stderr.writeln( "B.func in block" );
     }
     body
     {
         stderr.writeln( "B.func body block" );
         return x * 3;
     }
}

void main()
{
     auto a = new B;
     auto v = a.func( 3.14 );
}

[output]

A.func in block
B.func body block

In class B 'in' block not called, but if add 'out' block it 
called both for A and B classes.
Dec 17 2014
parent reply "John Colvin" <john.loughran.colvin gmail.com> writes:
On Wednesday, 17 December 2014 at 21:07:12 UTC, Oleg wrote:

 Is this behavior normal or it's bug?

 [code]

 import std.stdio;

 class A
 {
     float func( float x )
     in
     {
         assert( x > 0 );
         stderr.writeln( "A.func in block" );
     }
     body
     {
         stderr.writeln( "A.func body block" );
         return x / 3;
     }
 }

 class B : A
 {
     override float func( float x )
     in
     {
         assert( x < 10 );
         stderr.writeln( "B.func in block" );
     }
     body
     {
         stderr.writeln( "B.func body block" );
         return x * 3;
     }
 }

 void main()
 {
     auto a = new B;
     auto v = a.func( 3.14 );
 }

 [output]

 A.func in block
 B.func body block

 In class B 'in' block not called, but if add 'out' block it 
 called both for A and B classes.


Only 1 of the in contracts must be satisfied and it appears that 
in this case the A.foo one was checked first. Seeing as it 
passed, there was no need to check the B.foo in contract. Imagine 
it as an OR of in contracts.

All out contracts must be satisfied, hence both must be run to 
check. Images it as an AND of the out contracts.

See http://dlang.org/contracts.html
Dec 17 2014
parent "John Colvin" <john.loughran.colvin gmail.com> writes:
On Wednesday, 17 December 2014 at 21:17:57 UTC, John Colvin wrote:

 On Wednesday, 17 December 2014 at 21:07:12 UTC, Oleg wrote:

 Is this behavior normal or it's bug?

 [code]

 import std.stdio;

 class A
 {
    float func( float x )
    in
    {
        assert( x > 0 );
        stderr.writeln( "A.func in block" );
    }
    body
    {
        stderr.writeln( "A.func body block" );
        return x / 3;
    }
 }

 class B : A
 {
    override float func( float x )
    in
    {
        assert( x < 10 );
        stderr.writeln( "B.func in block" );
    }
    body
    {
        stderr.writeln( "B.func body block" );
        return x * 3;
    }
 }

 void main()
 {
    auto a = new B;
    auto v = a.func( 3.14 );
 }

 [output]

 A.func in block
 B.func body block

 In class B 'in' block not called, but if add 'out' block it 
 called both for A and B classes.


 Only 1 of the in contracts must be satisfied and it appears 
 that in this case the A.foo one was checked first. Seeing as it 
 passed, there was no need to check the B.foo in contract. 
 Imagine it as an OR of in contracts.

 All out contracts must be satisfied, hence both must be run to 
 check. Images it as an AND of the out contracts.

 See http://dlang.org/contracts.html


A corollary of this is that you have to be careful about 
side-effects inside contracts. Normally contracts should be pure.
Dec 17 2014