In C++ throw is an expression

Robert Smallshire — Fri, 31 Jul 2009 11:11:45 +0000

After 15 years programming in C++, I was surprised to discover today that throw in C++ is an expression rather than a statement. As a result, throw may be used as part of larger expressions.

int x = 5;
int y = x > 4 ? x : throw std::out_of_range;

The only use I’ve found for this — and in fact the speculative attempt by which I discovered it — is range checking within constructor initializer lists.

RangeChecked::RangeChecked(int x) :
    int_member(x > 0 ? x : throw std::out_of_range)
{
}

It’s academic what the type of a throw expression is, since it will never be returned, but for type-checking purposes the compiler seems to be happy to use it in place of any type.

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In C++ throw is an expression