On 7/30/2014 12:54 AM, David Bregman wrote:
On Wednesday, 30 July 2014 at 03:32:50 UTC, Walter Bright wrote:
I don't either. I still have no idea what the difference between assume(i<6)
and assert(i<6) is supposed to be.
assert:
is a runtime check of the condition.
is a debugging/correctness checking feature.
is used when the expression is believed true, but is not proven so.
(if it was proven, then there is no purpose in asserting it with a redundant
runtime check that is guaranteed to never activate.)
assume:
passes a hint to the optimizer to allow better code generation.
is used when the expression is proven to be true (by the programmer, like
@trusted).
It still means the same thing as assert.
The only relation between the two is that if a runtime check for (x) is inserted
at some point, it is safe to insert an assume(x) statement afterwards, because x
is known true at that point.
I.e. they're the same thing.
If assert degenerates to assume in release mode, any bugs in the program could
potentially cause a lot more brittleness and unexpected/undefined behavior than
they otherwise would have. In particular, code generation based on invalid
assumptions could be memory unsafe.
Which is why assert can also do a runtime check.