Re: Why is the iterator pass-by-value in the STL?
On 16 Nov., 17:59, Ruki <war...@gmail.com> wrote:
Why is the iterator pass-by-value in the STL?
I think it is more efficient and safe by passing a const
reference,isn't it?
void func(const_iterator first, const_iterator last);
void func(const_iterator const& first, const_iterator const& last);
Who can tell me what form is better?
This question can not be answered on a general
base. A rough rule would be to reason that
expensive-to-copy objects often take advantage
of by-reference parameters, while cheap-to-copy
objects usually are more efficiently transported
by-value. Iterators - generalizations of pointers
- are usually expected to be copied cheaply.
If a function parameter is taken by value, this
makes it usually easier for the compiler to optimize
the code. A copy has no "history", but a reference
must be back-tracked by the compiler to find out,
whether any optimization done on this entity
can be performed or not.
Btw.: Should you have the book "C++ Template - The
Complete Guid" near to you: Read section 22.1 (1st
edition) which nicely explains the difference between
direct and indirect calls. This explains the advantage
of using function objects by value instead of taking
function pointers. This is a similar reason for by-value
parameters reasoned on the level of functions objects.
HTH & Greetings from Bremen,
Daniel Kr?gler
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