What is a concise notation for a range based for loop iterating over a few tuples
Is there a simpler (shorter) way to write this code snippet as a loop:
for (auto [a, b]: {pair<int, int>{1, 2}, pair<int, int>{3, 4}})
foo(a, b);
Preferably making the initializer list as close as possible to this form, which doesn't compile:
for (auto [a, b]: {{1, 2}, {3, 4}})
foo(a, b);
c++ c++17
add a comment |
Is there a simpler (shorter) way to write this code snippet as a loop:
for (auto [a, b]: {pair<int, int>{1, 2}, pair<int, int>{3, 4}})
foo(a, b);
Preferably making the initializer list as close as possible to this form, which doesn't compile:
for (auto [a, b]: {{1, 2}, {3, 4}})
foo(a, b);
c++ c++17
cough macr cough o...
– YSC
Nov 23 '18 at 10:34
4
do { foo(1, 2); foo(3, 4); } while (false);
;-)
– Jarod42
Nov 23 '18 at 10:36
@Jarod42 You are legally correct! ;-)
– Paul Jurczak
Nov 23 '18 at 10:39
add a comment |
Is there a simpler (shorter) way to write this code snippet as a loop:
for (auto [a, b]: {pair<int, int>{1, 2}, pair<int, int>{3, 4}})
foo(a, b);
Preferably making the initializer list as close as possible to this form, which doesn't compile:
for (auto [a, b]: {{1, 2}, {3, 4}})
foo(a, b);
c++ c++17
Is there a simpler (shorter) way to write this code snippet as a loop:
for (auto [a, b]: {pair<int, int>{1, 2}, pair<int, int>{3, 4}})
foo(a, b);
Preferably making the initializer list as close as possible to this form, which doesn't compile:
for (auto [a, b]: {{1, 2}, {3, 4}})
foo(a, b);
c++ c++17
c++ c++17
asked Nov 23 '18 at 10:18
Paul JurczakPaul Jurczak
3,0462646
3,0462646
cough macr cough o...
– YSC
Nov 23 '18 at 10:34
4
do { foo(1, 2); foo(3, 4); } while (false);
;-)
– Jarod42
Nov 23 '18 at 10:36
@Jarod42 You are legally correct! ;-)
– Paul Jurczak
Nov 23 '18 at 10:39
add a comment |
cough macr cough o...
– YSC
Nov 23 '18 at 10:34
4
do { foo(1, 2); foo(3, 4); } while (false);
;-)
– Jarod42
Nov 23 '18 at 10:36
@Jarod42 You are legally correct! ;-)
– Paul Jurczak
Nov 23 '18 at 10:39
cough macr cough o...
– YSC
Nov 23 '18 at 10:34
cough macr cough o...
– YSC
Nov 23 '18 at 10:34
4
4
do { foo(1, 2); foo(3, 4); } while (false);
;-)– Jarod42
Nov 23 '18 at 10:36
do { foo(1, 2); foo(3, 4); } while (false);
;-)– Jarod42
Nov 23 '18 at 10:36
@Jarod42 You are legally correct! ;-)
– Paul Jurczak
Nov 23 '18 at 10:39
@Jarod42 You are legally correct! ;-)
– Paul Jurczak
Nov 23 '18 at 10:39
add a comment |
4 Answers
4
active
oldest
votes
You might do the following in C++17 thanks to deduction guide:
for (auto [a, b]: {std::pair{1, 2}, std::pair{3, 4}})
foo(a, b);
or even
for (auto [a, b]: {std::pair{1, 2}, {3, 4}})
foo(a, b);
Beautiful! Since I usually dispense withstd::
, your solution is literally the most concise and flexible one.
– Paul Jurczak
Nov 23 '18 at 10:56
Along these lines:for (auto [i, j, k]: {tuple{.1, .5, 5}, tuple{.4, .5, 6}})
– Paul Jurczak
Nov 23 '18 at 11:13
2
@PaulJurczak - You can go one shorter. Only the first item must explicitly be a pair. The second one will be deduced based of the first.
– StoryTeller
Nov 23 '18 at 12:08
This scales terribly though...
– rubenvb
Nov 23 '18 at 15:03
@rubenvb What do you mean by scales terribly? Compile time penalty?
– Paul Jurczak
Nov 23 '18 at 21:32
|
show 1 more comment
As C++ is a strongly typed language, there are limits to the fuzziness you can expect from the compiler deduced types. Two levels of unspecified braces is an example of this.
You can make it shorter by using a simple typedef:
using pair_list = std::initializer_list<std::pair<int, int>>;
for (auto [a, b]: pair_list{{1, 2}, {3, 4}})
foo(a, b);
Live demo here. You can optimize/choose the temporary's type as you wish.
2
Oh. And there I was mucking around with classes and deduction guides.
– Quentin
Nov 23 '18 at 10:35
add a comment |
There is a shorter way to do it which involves construction of a temporary std::map
.
You can do something like this:
for (auto [a, b]: map<int, int>{{1, 2}, {3, 4}})
foo(a, b);
This compiles. See it here.
Or as @Jarod42 suggested, you can use std::initializer_list<std::pair<int, int>>
as well.
for (auto [a, b]: std::initializer_list<std::pair<int, int>>{{1, 2}, {3, 4}})
You will have to type a bit more. :)
std::initializer_list<std::pair<int, int>>
should do the job too.
– Jarod42
Nov 23 '18 at 10:34
@Jarod42: Thanks. Updated.
– P.W
Nov 23 '18 at 10:37
map<int, int>
looks good, but will probably be a performance killer in an inner loop.
– Paul Jurczak
Nov 23 '18 at 10:45
@PaulJurczak: Yeah, I was going for the shortest. :)
– P.W
Nov 23 '18 at 10:50
add a comment |
Still a bit verbose, but this template might be of help:
template <class T>
constexpr auto asPairs(std::initializer_list<std::pair<T, T>> args)
{
return args;
}
It can be instantiated and used like the following.
for (auto [a, b] : asPairs<int>({{1, 2}, {3, 4}}))
foo(a, b);
add a comment |
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
You might do the following in C++17 thanks to deduction guide:
for (auto [a, b]: {std::pair{1, 2}, std::pair{3, 4}})
foo(a, b);
or even
for (auto [a, b]: {std::pair{1, 2}, {3, 4}})
foo(a, b);
Beautiful! Since I usually dispense withstd::
, your solution is literally the most concise and flexible one.
– Paul Jurczak
Nov 23 '18 at 10:56
Along these lines:for (auto [i, j, k]: {tuple{.1, .5, 5}, tuple{.4, .5, 6}})
– Paul Jurczak
Nov 23 '18 at 11:13
2
@PaulJurczak - You can go one shorter. Only the first item must explicitly be a pair. The second one will be deduced based of the first.
– StoryTeller
Nov 23 '18 at 12:08
This scales terribly though...
– rubenvb
Nov 23 '18 at 15:03
@rubenvb What do you mean by scales terribly? Compile time penalty?
– Paul Jurczak
Nov 23 '18 at 21:32
|
show 1 more comment
You might do the following in C++17 thanks to deduction guide:
for (auto [a, b]: {std::pair{1, 2}, std::pair{3, 4}})
foo(a, b);
or even
for (auto [a, b]: {std::pair{1, 2}, {3, 4}})
foo(a, b);
Beautiful! Since I usually dispense withstd::
, your solution is literally the most concise and flexible one.
– Paul Jurczak
Nov 23 '18 at 10:56
Along these lines:for (auto [i, j, k]: {tuple{.1, .5, 5}, tuple{.4, .5, 6}})
– Paul Jurczak
Nov 23 '18 at 11:13
2
@PaulJurczak - You can go one shorter. Only the first item must explicitly be a pair. The second one will be deduced based of the first.
– StoryTeller
Nov 23 '18 at 12:08
This scales terribly though...
– rubenvb
Nov 23 '18 at 15:03
@rubenvb What do you mean by scales terribly? Compile time penalty?
– Paul Jurczak
Nov 23 '18 at 21:32
|
show 1 more comment
You might do the following in C++17 thanks to deduction guide:
for (auto [a, b]: {std::pair{1, 2}, std::pair{3, 4}})
foo(a, b);
or even
for (auto [a, b]: {std::pair{1, 2}, {3, 4}})
foo(a, b);
You might do the following in C++17 thanks to deduction guide:
for (auto [a, b]: {std::pair{1, 2}, std::pair{3, 4}})
foo(a, b);
or even
for (auto [a, b]: {std::pair{1, 2}, {3, 4}})
foo(a, b);
edited Nov 23 '18 at 15:14
answered Nov 23 '18 at 10:39
Jarod42Jarod42
119k12104189
119k12104189
Beautiful! Since I usually dispense withstd::
, your solution is literally the most concise and flexible one.
– Paul Jurczak
Nov 23 '18 at 10:56
Along these lines:for (auto [i, j, k]: {tuple{.1, .5, 5}, tuple{.4, .5, 6}})
– Paul Jurczak
Nov 23 '18 at 11:13
2
@PaulJurczak - You can go one shorter. Only the first item must explicitly be a pair. The second one will be deduced based of the first.
– StoryTeller
Nov 23 '18 at 12:08
This scales terribly though...
– rubenvb
Nov 23 '18 at 15:03
@rubenvb What do you mean by scales terribly? Compile time penalty?
– Paul Jurczak
Nov 23 '18 at 21:32
|
show 1 more comment
Beautiful! Since I usually dispense withstd::
, your solution is literally the most concise and flexible one.
– Paul Jurczak
Nov 23 '18 at 10:56
Along these lines:for (auto [i, j, k]: {tuple{.1, .5, 5}, tuple{.4, .5, 6}})
– Paul Jurczak
Nov 23 '18 at 11:13
2
@PaulJurczak - You can go one shorter. Only the first item must explicitly be a pair. The second one will be deduced based of the first.
– StoryTeller
Nov 23 '18 at 12:08
This scales terribly though...
– rubenvb
Nov 23 '18 at 15:03
@rubenvb What do you mean by scales terribly? Compile time penalty?
– Paul Jurczak
Nov 23 '18 at 21:32
Beautiful! Since I usually dispense with
std::
, your solution is literally the most concise and flexible one.– Paul Jurczak
Nov 23 '18 at 10:56
Beautiful! Since I usually dispense with
std::
, your solution is literally the most concise and flexible one.– Paul Jurczak
Nov 23 '18 at 10:56
Along these lines:
for (auto [i, j, k]: {tuple{.1, .5, 5}, tuple{.4, .5, 6}})
– Paul Jurczak
Nov 23 '18 at 11:13
Along these lines:
for (auto [i, j, k]: {tuple{.1, .5, 5}, tuple{.4, .5, 6}})
– Paul Jurczak
Nov 23 '18 at 11:13
2
2
@PaulJurczak - You can go one shorter. Only the first item must explicitly be a pair. The second one will be deduced based of the first.
– StoryTeller
Nov 23 '18 at 12:08
@PaulJurczak - You can go one shorter. Only the first item must explicitly be a pair. The second one will be deduced based of the first.
– StoryTeller
Nov 23 '18 at 12:08
This scales terribly though...
– rubenvb
Nov 23 '18 at 15:03
This scales terribly though...
– rubenvb
Nov 23 '18 at 15:03
@rubenvb What do you mean by scales terribly? Compile time penalty?
– Paul Jurczak
Nov 23 '18 at 21:32
@rubenvb What do you mean by scales terribly? Compile time penalty?
– Paul Jurczak
Nov 23 '18 at 21:32
|
show 1 more comment
As C++ is a strongly typed language, there are limits to the fuzziness you can expect from the compiler deduced types. Two levels of unspecified braces is an example of this.
You can make it shorter by using a simple typedef:
using pair_list = std::initializer_list<std::pair<int, int>>;
for (auto [a, b]: pair_list{{1, 2}, {3, 4}})
foo(a, b);
Live demo here. You can optimize/choose the temporary's type as you wish.
2
Oh. And there I was mucking around with classes and deduction guides.
– Quentin
Nov 23 '18 at 10:35
add a comment |
As C++ is a strongly typed language, there are limits to the fuzziness you can expect from the compiler deduced types. Two levels of unspecified braces is an example of this.
You can make it shorter by using a simple typedef:
using pair_list = std::initializer_list<std::pair<int, int>>;
for (auto [a, b]: pair_list{{1, 2}, {3, 4}})
foo(a, b);
Live demo here. You can optimize/choose the temporary's type as you wish.
2
Oh. And there I was mucking around with classes and deduction guides.
– Quentin
Nov 23 '18 at 10:35
add a comment |
As C++ is a strongly typed language, there are limits to the fuzziness you can expect from the compiler deduced types. Two levels of unspecified braces is an example of this.
You can make it shorter by using a simple typedef:
using pair_list = std::initializer_list<std::pair<int, int>>;
for (auto [a, b]: pair_list{{1, 2}, {3, 4}})
foo(a, b);
Live demo here. You can optimize/choose the temporary's type as you wish.
As C++ is a strongly typed language, there are limits to the fuzziness you can expect from the compiler deduced types. Two levels of unspecified braces is an example of this.
You can make it shorter by using a simple typedef:
using pair_list = std::initializer_list<std::pair<int, int>>;
for (auto [a, b]: pair_list{{1, 2}, {3, 4}})
foo(a, b);
Live demo here. You can optimize/choose the temporary's type as you wish.
answered Nov 23 '18 at 10:34
rubenvbrubenvb
54k22140261
54k22140261
2
Oh. And there I was mucking around with classes and deduction guides.
– Quentin
Nov 23 '18 at 10:35
add a comment |
2
Oh. And there I was mucking around with classes and deduction guides.
– Quentin
Nov 23 '18 at 10:35
2
2
Oh. And there I was mucking around with classes and deduction guides.
– Quentin
Nov 23 '18 at 10:35
Oh. And there I was mucking around with classes and deduction guides.
– Quentin
Nov 23 '18 at 10:35
add a comment |
There is a shorter way to do it which involves construction of a temporary std::map
.
You can do something like this:
for (auto [a, b]: map<int, int>{{1, 2}, {3, 4}})
foo(a, b);
This compiles. See it here.
Or as @Jarod42 suggested, you can use std::initializer_list<std::pair<int, int>>
as well.
for (auto [a, b]: std::initializer_list<std::pair<int, int>>{{1, 2}, {3, 4}})
You will have to type a bit more. :)
std::initializer_list<std::pair<int, int>>
should do the job too.
– Jarod42
Nov 23 '18 at 10:34
@Jarod42: Thanks. Updated.
– P.W
Nov 23 '18 at 10:37
map<int, int>
looks good, but will probably be a performance killer in an inner loop.
– Paul Jurczak
Nov 23 '18 at 10:45
@PaulJurczak: Yeah, I was going for the shortest. :)
– P.W
Nov 23 '18 at 10:50
add a comment |
There is a shorter way to do it which involves construction of a temporary std::map
.
You can do something like this:
for (auto [a, b]: map<int, int>{{1, 2}, {3, 4}})
foo(a, b);
This compiles. See it here.
Or as @Jarod42 suggested, you can use std::initializer_list<std::pair<int, int>>
as well.
for (auto [a, b]: std::initializer_list<std::pair<int, int>>{{1, 2}, {3, 4}})
You will have to type a bit more. :)
std::initializer_list<std::pair<int, int>>
should do the job too.
– Jarod42
Nov 23 '18 at 10:34
@Jarod42: Thanks. Updated.
– P.W
Nov 23 '18 at 10:37
map<int, int>
looks good, but will probably be a performance killer in an inner loop.
– Paul Jurczak
Nov 23 '18 at 10:45
@PaulJurczak: Yeah, I was going for the shortest. :)
– P.W
Nov 23 '18 at 10:50
add a comment |
There is a shorter way to do it which involves construction of a temporary std::map
.
You can do something like this:
for (auto [a, b]: map<int, int>{{1, 2}, {3, 4}})
foo(a, b);
This compiles. See it here.
Or as @Jarod42 suggested, you can use std::initializer_list<std::pair<int, int>>
as well.
for (auto [a, b]: std::initializer_list<std::pair<int, int>>{{1, 2}, {3, 4}})
You will have to type a bit more. :)
There is a shorter way to do it which involves construction of a temporary std::map
.
You can do something like this:
for (auto [a, b]: map<int, int>{{1, 2}, {3, 4}})
foo(a, b);
This compiles. See it here.
Or as @Jarod42 suggested, you can use std::initializer_list<std::pair<int, int>>
as well.
for (auto [a, b]: std::initializer_list<std::pair<int, int>>{{1, 2}, {3, 4}})
You will have to type a bit more. :)
edited Nov 23 '18 at 10:37
answered Nov 23 '18 at 10:33
P.WP.W
17.8k41657
17.8k41657
std::initializer_list<std::pair<int, int>>
should do the job too.
– Jarod42
Nov 23 '18 at 10:34
@Jarod42: Thanks. Updated.
– P.W
Nov 23 '18 at 10:37
map<int, int>
looks good, but will probably be a performance killer in an inner loop.
– Paul Jurczak
Nov 23 '18 at 10:45
@PaulJurczak: Yeah, I was going for the shortest. :)
– P.W
Nov 23 '18 at 10:50
add a comment |
std::initializer_list<std::pair<int, int>>
should do the job too.
– Jarod42
Nov 23 '18 at 10:34
@Jarod42: Thanks. Updated.
– P.W
Nov 23 '18 at 10:37
map<int, int>
looks good, but will probably be a performance killer in an inner loop.
– Paul Jurczak
Nov 23 '18 at 10:45
@PaulJurczak: Yeah, I was going for the shortest. :)
– P.W
Nov 23 '18 at 10:50
std::initializer_list<std::pair<int, int>>
should do the job too.– Jarod42
Nov 23 '18 at 10:34
std::initializer_list<std::pair<int, int>>
should do the job too.– Jarod42
Nov 23 '18 at 10:34
@Jarod42: Thanks. Updated.
– P.W
Nov 23 '18 at 10:37
@Jarod42: Thanks. Updated.
– P.W
Nov 23 '18 at 10:37
map<int, int>
looks good, but will probably be a performance killer in an inner loop.– Paul Jurczak
Nov 23 '18 at 10:45
map<int, int>
looks good, but will probably be a performance killer in an inner loop.– Paul Jurczak
Nov 23 '18 at 10:45
@PaulJurczak: Yeah, I was going for the shortest. :)
– P.W
Nov 23 '18 at 10:50
@PaulJurczak: Yeah, I was going for the shortest. :)
– P.W
Nov 23 '18 at 10:50
add a comment |
Still a bit verbose, but this template might be of help:
template <class T>
constexpr auto asPairs(std::initializer_list<std::pair<T, T>> args)
{
return args;
}
It can be instantiated and used like the following.
for (auto [a, b] : asPairs<int>({{1, 2}, {3, 4}}))
foo(a, b);
add a comment |
Still a bit verbose, but this template might be of help:
template <class T>
constexpr auto asPairs(std::initializer_list<std::pair<T, T>> args)
{
return args;
}
It can be instantiated and used like the following.
for (auto [a, b] : asPairs<int>({{1, 2}, {3, 4}}))
foo(a, b);
add a comment |
Still a bit verbose, but this template might be of help:
template <class T>
constexpr auto asPairs(std::initializer_list<std::pair<T, T>> args)
{
return args;
}
It can be instantiated and used like the following.
for (auto [a, b] : asPairs<int>({{1, 2}, {3, 4}}))
foo(a, b);
Still a bit verbose, but this template might be of help:
template <class T>
constexpr auto asPairs(std::initializer_list<std::pair<T, T>> args)
{
return args;
}
It can be instantiated and used like the following.
for (auto [a, b] : asPairs<int>({{1, 2}, {3, 4}}))
foo(a, b);
answered Nov 23 '18 at 10:34
lubgrlubgr
14.7k32152
14.7k32152
add a comment |
add a comment |
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cough macr cough o...
– YSC
Nov 23 '18 at 10:34
4
do { foo(1, 2); foo(3, 4); } while (false);
;-)– Jarod42
Nov 23 '18 at 10:36
@Jarod42 You are legally correct! ;-)
– Paul Jurczak
Nov 23 '18 at 10:39