[phobos] enforce() vs. assert() for range primitives

David Simcha dsimcha at gmail.com
Sat Aug 21 11:52:54 PDT 2010

It seems like the consensus here is that, for range primitives, assert() 
is the way to go.  I'd like to commit the changes in time for the next 
release, but I'd like to have Andrei's nod first b/c he's been quiet 
throughout this discussion and he's the main designer of std.range and 

On 8/18/2010 6:49 PM, David Simcha wrote:
> While I was debugging std.range and std.algorithm I noticed that 
> there's tons of inconsistency about when enforce() vs. assert() is 
> used for checking input to range primitives.  I think this needs to be 
> made consistent, and there are good arguments for both.
> enforce() is arguably the way to go because we're dealing with an 
> external API, not internal consistency checks.  According to the 
> guidelines in TDPL input external to an API should be checked even in 
> release mode.
> On the other hand, assert() is arguably the way to go because ranges 
> are supposed to be a very efficient abstraction.  Having enforce() in 
> range primitives that look like they should be very fast, inlined 
> functions is just bad practice.  For example, some benchmarks I did 
> awhile back showed that the use of enforce() and its effect on 
> inlining can make using ranges slower than using opApply.  
> Furthermore, if you're stacking several higher-order ranges, i.e. 
> filter!"a > 0"(map!"a * a"(retro(someArray))) the checks may be 
> redundant.  Lastly, since arrays are the canonical range, omitting 
> release mode checks in library-defined ranges would make them 
> consistent with arrays.
> Generally when I was debugging I tried to be locally consistent, i.e. 
> use whatever was used elsewhere in the same range.  This meant being 
> globally inconsistent.  Now that I've thought about it, my vote is for 
> using assert() consistently for range primitives.  If ranges are 
> filled with tons of safety checks that have significant performance 
> costs and can't be disabled even in release mode, they will have 
> failed in their goal of providing a lightweight, efficient 
> abstraction.  enforce() can be used for things that are intended to be 
> called much less frequently, like constructors.  Comments?

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