assert(obj) is an atrocity

Martin Nowak dawg at
Tue Nov 8 16:18:38 PST 2011

On Tue, 08 Nov 2011 23:35:33 +0100, Alex Rønne Petersen  
<xtzgzorex at> wrote:

> Hi,
> As the title suggests, I'm going to be rather blunt about this.  
> assert(obj) testing the invariant *without* doing a null check is insane  
> for the following reasons:
> 1) It is not what a user expects. It is *unintuitive*.
> 2) assert(!obj) does an is-null check. assert(obj) is a completely  
> broken opposite of this.
> 3) No AssertError is thrown, which is the entire point of the built-in  
> assert().
> 4) The few added instructions for the null check hardly matter in a  
> *debug* build of all things.
> I don't mind assert(obj) testing the invariant of obj. In fact, that  
> very much makes sense. But please, please, *please* check the object for  
> null first. This is a random inconsistency in the language with no other  
> justification than "seg faults are convenient in a debugger". By the  
> same logic, we might as well not have array bounds checks. However, the  
> state of things is that array bounds checks are emitted by default and  
> users can disable them for e.g. a release build. I don't see why this  
> case is any different.
> - Alex

It does check for null.
Only it's a runtime support function (_d_invariant) and druntime is likely
compiled without assertions. Are you really suggesting to add a null check  
every method call?


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