<s>
In	O
generic	B-Language
programming	I-Language
,	O
a	O
concept	O
is	O
a	O
description	O
of	O
supported	O
operations	O
on	O
a	O
type	O
,	O
including	O
syntax	O
and	O
semantics	O
.	O
</s>
<s>
In	O
this	O
way	O
,	O
concepts	B-Language
are	O
related	O
to	O
abstract	O
types	O
but	O
concepts	B-Language
do	O
not	O
require	O
a	O
subtype	O
relationship	O
.	O
</s>
<s>
The	O
term	O
was	O
in	O
use	O
as	O
early	O
as	O
1998	O
for	O
STL	B-Application
,	O
as	O
this	O
was	O
one	O
of	O
the	O
first	O
libraries	O
that	O
extensively	O
used	O
templates	B-Application
.	O
</s>
<s>
The	O
term	O
concept	O
(	O
and	O
its	O
popularization	O
)	O
is	O
credited	O
to	O
Alexander	O
Stepanov	O
,	O
the	O
primary	O
designer	O
of	O
the	O
STL	B-Application
.	O
</s>
<s>
In	O
the	O
C++	B-Language
1998	O
standard	O
,	O
the	O
Concept	O
term	O
was	O
introduced	O
to	O
name	O
just	O
a	O
simple	O
description	O
of	O
the	O
requirements	O
for	O
particular	O
type	O
,	O
usually	O
being	O
a	O
template	B-Application
parameter	O
.	O
</s>
<s>
There	O
was	O
a	O
proposal	O
to	O
add	O
concepts	B-Language
as	O
an	O
explicit	O
language	O
feature	O
in	O
C++11	B-Language
,	O
though	O
it	O
was	O
rejected	O
as	O
"	O
not	O
ready	O
"	O
.	O
</s>
<s>
C++20	B-Language
eventually	O
accepted	O
the	O
refined	O
design	O
of	O
concept	O
.	O
</s>
<s>
As	O
generics	O
in	O
Java	B-Language
and	O
C#	B-Application
have	O
some	O
similarities	O
to	O
C++'s	O
templates	B-Application
,	O
the	O
role	O
of	O
concepts	B-Language
there	O
is	O
played	O
by	O
interfaces	B-Application
.	O
</s>
<s>
However	O
,	O
there	O
is	O
one	O
important	O
difference	O
between	O
concepts	B-Language
and	O
interfaces	B-Application
:	O
when	O
a	O
template	B-Application
parameter	O
is	O
required	O
to	O
implement	O
a	O
particular	O
interface	O
,	O
the	O
matching	O
type	O
can	O
only	O
be	O
a	O
class	O
that	O
implements	B-Language
(	O
explicitly	O
)	O
that	O
interface	O
.	O
</s>
<s>
Concepts	B-Language
bring	O
more	O
flexibility	O
because	O
they	O
can	O
be	O
satisfied	O
in	O
two	O
ways	O
:	O
</s>
<s>
But	O
the	O
C#	B-Application
language	O
has	O
several	O
constructs	O
where	O
the	O
used	O
type	O
does	O
not	O
need	O
to	O
explicitly	O
implement	O
a	O
defined	O
interface	O
,	O
it	O
is	O
only	O
required	O
to	O
match	O
the	O
respective	O
pattern	O
(	O
however	O
,	O
these	O
patterns	O
are	O
not	O
called	O
concepts	B-Language
)	O
.	O
</s>
<s>
the	O
foreach	O
iteration	O
statement	O
allows	O
the	O
iterated	O
object	O
to	O
be	O
of	O
any	O
type	O
,	O
as	O
long	O
as	O
it	O
implements	B-Language
an	O
appropriate	O
GetEnumerator	O
method	O
.	O
</s>
<s>
Another	O
language	O
implementing	O
something	O
very	O
similar	O
to	O
concepts	B-Language
is	O
Haskell	B-Language
,	O
where	O
the	O
feature	O
is	O
called	O
type	O
classes	O
.	O
</s>
<s>
If	O
a	O
type	O
I	O
satisfies	O
the	O
Trivial	O
Iterator	O
concept	O
in	O
C++	B-Language
,	O
and	O
i	O
is	O
of	O
type	O
I	O
,	O
the	O
following	O
are	O
valid	O
expressions	O
with	O
corresponding	O
semantics	O
:	O
</s>
