digitalmars.D.learn - auto
- Hoenir <mrmocool gmx.de> Jun 20 2007
- Derek Parnell <derek psych.ward> Jun 20 2007
- Ary Manzana <ary esperanto.org.ar> Jun 20 2007
- BCS <BCS pathlink.com> Jun 20 2007
- Derek Parnell <derek nomail.afraid.org> Jun 20 2007
- Bill Baxter <dnewsgroup billbaxter.com> Jun 21 2007
- Frits van Bommel <fvbommel REMwOVExCAPSs.nl> Jun 22 2007
- Ary Manzana <ary esperanto.org.ar> Jun 22 2007
- Jari-Matti =?ISO-8859-1?Q?M=E4kel=E4?= <jmjmak utu.fi.invalid> Jun 20 2007
- "Jarrett Billingsley" <kb3ctd2 yahoo.com> Jun 20 2007
- Hoenir <mrmocool gmx.de> Jun 20 2007
- janderson <askme me.com> Jun 21 2007
- janderson <askme me.com> Jun 21 2007
I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
Jun 20 2007
On Wed, 20 Jun 2007 14:20:43 +0200, Hoenir wrote:I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
auto y = someFunc(); // What type is it now? -- Derek Parnell Melbourne, Australia "Justice for David Hicks!" skype: derek.j.parnell
Jun 20 2007
Derek Parnell escribió:On Wed, 20 Jun 2007 14:20:43 +0200, Hoenir wrote:I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
auto y = someFunc(); // What type is it now?
// What can you do with y now, if you don't know the type?
Jun 20 2007
BCS <BCS pathlink.com> Ary Manzana wrote:Derek Parnell escribió:On Wed, 20 Jun 2007 14:20:43 +0200, Hoenir wrote:I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
auto y = someFunc(); // What type is it now?
// What can you do with y now, if you don't know the type?
whatever you want auto z = y * 2; auto x = z*y; return x + y + z; With a little care and a working knowledge of the typing rules of expressions you can get a lot done without ever using a actual type. This is of a lot of use if you are doing template code where you really can't known the type until compile time.
Jun 20 2007
On Wed, 20 Jun 2007 21:37:44 -0200, Ary Manzana wrote:Derek Parnell escribió:On Wed, 20 Jun 2007 14:20:43 +0200, Hoenir wrote:I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
auto y = someFunc(); // What type is it now?
// What can you do with y now, if you don't know the type?
Pass it to a function that does know its type. void funcA(int X) { } void funcA(float X) { } void funcA(char[] X) { } auto y = someFunc(); funcA(y); -- Derek (skype: derek.j.parnell) Melbourne, Australia 21/06/2007 12:30:47 PM
Jun 20 2007
Derek Parnell wrote:On Wed, 20 Jun 2007 21:37:44 -0200, Ary Manzana wrote:Derek Parnell escribió:On Wed, 20 Jun 2007 14:20:43 +0200, Hoenir wrote:I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
Pass it to a function that does know its type.
I *think* the point was just that the code becomes less readable without any obvious indication of what type you've got. Sure you can do all the same things you could do it the type were explicit, but someone else asked to fix this code is going to have to track down "someFunc()" to see what it returns. Lacking any particular extenuating circumstances, I agree that that making types explicit is better than using auto. But auto makes sense when 1) the actual type is a built-in (auto x = foo.length) 2) the actual type is obvious (auto x = new MyClass()) 3) the actual type is huge/untypeable like ( Node!(Node!(Node!(Expr!(Terminal!(1),Terminal!(2))))) x = expr!(); 4) the actual type is unknowable (some template usages) or 5) when you're in a real hurry and don't have time to figure out what the actual type is. :-) --bb
Jun 21 2007
Bill Baxter wrote:Lacking any particular extenuating circumstances, I agree that that making types explicit is better than using auto. But auto makes sense when
How about: 6) When the actual type may change later, and you want to make sure the variable is of the right type? I've often found this to be very useful, especially since some implicit conversions can change the value (e.g. long -> int, signed/unsigned).
Jun 22 2007
Bill Baxter escribió:Derek Parnell wrote:On Wed, 20 Jun 2007 21:37:44 -0200, Ary Manzana wrote:Derek Parnell escribió:On Wed, 20 Jun 2007 14:20:43 +0200, Hoenir wrote:I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
Pass it to a function that does know its type.
I *think* the point was just that the code becomes less readable without any obvious indication of what type you've got. Sure you can do all the same things you could do it the type were explicit, but someone else asked to fix this code is going to have to track down "someFunc()" to see what it returns.
Thanks for this! This is exacly my thought, although I couldn't have expressed myself that well. I also agree with the situations you describe below, and also with number 6 of Frits. I'll not use it anywhere else, since having the type is more self documenting in a function.Lacking any particular extenuating circumstances, I agree that that making types explicit is better than using auto. But auto makes sense when 1) the actual type is a built-in (auto x = foo.length) 2) the actual type is obvious (auto x = new MyClass()) 3) the actual type is huge/untypeable like ( Node!(Node!(Node!(Expr!(Terminal!(1),Terminal!(2))))) x = expr!(); 4) the actual type is unknowable (some template usages) or 5) when you're in a real hurry and don't have time to figure out what the actual type is. :-) --bb
Jun 22 2007
Hoenir wrote:I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
One day you may want to write class foo(a = int, b = int) { } void main() { auto bar = new foo!(foo!( foo!(foo!(), foo!()), foo!(foo!(), foo!()) ), foo!(foo!(), foo!())); }
Jun 20 2007
"Hoenir" <mrmocool gmx.de> wrote in message news:f5b64b$1aeq$1 digitalmars.com...I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
I agree in this case, and I think some people get a little type-inference-happy. But it's very useful in the cases that Derek and mwarning have posted, and I use it a lot in templates as well (rather than picking apart a complex type to determine the correct type for a variable, just use auto).
Jun 20 2007
Jarrett Billingsley wrote:I agree in this case, and I think some people get a little type-inference-happy. But it's very useful in the cases that Derek and mwarning have posted, and I use it a lot in templates as well (rather than picking apart a complex type to determine the correct type for a variable, just use auto).
Jun 20 2007
Hoenir wrote:I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
Its a generic/maintainable way of programming. It means you can change the types your using without having to change ever reference to it. It means you can copy paste or template a piece of code and have it work with little change. It gets even more useful in larger programs when you start to layer this sort of general programming. I hope that helps.
Jun 21 2007
janderson wrote:Hoenir wrote:I still can't get the purpose of "auto". I know it makes it possible to e.g. write "auto y = 4u;" but why not just "uint y = 4;"?
Its a generic/maintainable way of programming. It means you can change the types your using without having to change ever reference to it. It means you can copy paste or template a piece of code and have it work with little change. It gets even more useful in larger programs when you start to layer this sort of general programming. I hope that helps.
I should add, in the same vain (as others have mentioned in other ways), its useful for creating code that will work even when someone changes the interface. -Joel
Jun 21 2007