Re: [boost] [Boost-users] [review][fixed_string] FixedString review starts today

Zach Laine wrote:

On Wed, Nov 27, 2019 at 11:01 AM Peter Dimov via Boost wrote:

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Zach Laine wrote:

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Throwing when the capacity would be exceeded is wrong.

No, it's not. It's correct. It's a runtime error, not a programming time error.

Then why doesn't vector::operator[] throw? In either case, you know what the precondition is, and how to check it. That's what makes this a user error.

What makes op[] a user error is that the index rarely comes from external input. It typically comes from a variable that the programmer controls and program logic ensures is in range. Whereas when you += strings into a fixed capacity buffer, those are only occasionally programmer-supplied. Program logic is not violated if the input strings exceed the buffer. Or stated differently, if in 90% of the cases the correct use of a function would involve the programmer writing out the exact same if( !precondition ) throw exception(); thing that the function would have done itself were it throwing, the function should be throwing. Whereas when you do `for( int i = 0; i < n; ++i ) { something with v[i]; }`, you don't need to insert the above before each [].