digitalmars.D.learn - Array initializers and inheritance
- Max Bolingbroke (18/18) Oct 29 2006 Hi,
- Frank Benoit (keinfarbton) (13/13) Oct 29 2006 I think, the array initialization feature is not so nice. The array
- Chris Nicholson-Sauls (14/25) Oct 29 2006 You are correct that it takes its type from the first element. In the v...
- Bill Baxter (8/17) Oct 29 2006 To me that is fairly surprising behavior. I would expect the compiler
- Stewart Gordon (39/54) Nov 04 2006 That would create a parsing ambiguity.
Hi,
I have an array declared like so:
private GameObject[] _gameObjects;
And an inheritance hierarchy like this:
class Player : GameObject
{ ... }
class Target : GameObject
{ ... }
When I do this:
_gameObjects = [new Player(),
new Target(Direction.Up, 0, 0)];
I get a compile error (Target cannot be cast to Player). But when I do this:
_gameObjects = [cast(GameObject)(new Player()),
new Target(Direction.Up, 0, 0)];
It works! Is this by design? It is not clear to me from reading the
specification.
Thanks,
Max
Oct 29 2006
I think, the array initialization feature is not so nice. The array takes its type from the type of the first initializer. This is absolutely ugly. I would prefer if you can write this _gameObjects = new GameObject [ new Player(), new Target(Direction.Up, 0, 0)]; The second bad thing is, they tend to generate static arrays. So often you need to append a [] to convert the static array into a dynamic one. When generating D code, i use array initialization and cast every member to the type of the array element and append [] to every such initializer. This code looks really ugly. W Please rethink this syntax :) Or did I really missed the "good way of array initialization"?
Oct 29 2006
Frank Benoit (keinfarbton) wrote:I think, the array initialization feature is not so nice. The array takes its type from the type of the first initializer. This is absolutely ugly.You are correct that it takes its type from the first element. In the vast majority of cases (personal experience, might not be general) this hasn't been a problem. Still, I do feel a little antsy sometimes about putting that cast() at the beginning.I would prefer if you can write this _gameObjects = new GameObject [ new Player(), new Target(Direction.Up, 0, 0)];If one uses the CashewUtils array library (cashew.utils.array, available from DSource) then you can do: Still not perfeclty ideal, of course. This is my current personal (biased) preferance. ;)The second bad thing is, they tend to generate static arrays. So often you need to append a [] to convert the static array into a dynamic one.As far as I know, this shouldn't be neccesary. If I remember right, static arrays implicitly cast to dynamic arrays (but not the other way around). In fact, the extra [] at the end doesn't cast the array at all, but rather takes a full slice of it. Which still has the desired effect, but...When generating D code, i use array initialization and cast every member to the type of the array element and append [] to every such initializer. This code looks really ugly.You only have to cast the first one, as this is what determines the array's type. -- Chris Nicholson-Sauls
Oct 29 2006
Bill Baxter <dnewsgroup billbaxter.com> Chris Nicholson-Sauls wrote:Frank Benoit (keinfarbton) wrote:To me that is fairly surprising behavior. I would expect the compiler to look at *all* the values in the array literal and pick the type to use based on standard promotion rules ("integer promotions" and "usual arithmetic conversions" from http://www.digitalmars.com/d/type.html). I.e. [1, 2, 3, 4.0] should be double[4], not int[4]. Just like 1+2+3+4.0 is a double and not and int. --bbI think, the array initialization feature is not so nice. The array takes its type from the type of the first initializer. This is absolutely ugly.You are correct that it takes its type from the first element. In the vast majority of cases (personal experience, might not be general) this hasn't been a problem. Still, I do feel a little antsy sometimes about putting that cast() at the beginning.
Oct 29 2006
Frank Benoit (keinfarbton) wrote:I think, the array initialization feature is not so nice. The array takes its type from the type of the first initializer. This is absolutely ugly.That's not initialization, that's array literals.I would prefer if you can write this _gameObjects = new GameObject [ new Player(), new Target(Direction.Up, 0, 0)];That would create a parsing ambiguity. But I agree that it would be nice if you could give the type of an array literal explicitly. This syntax was suggested at least once: _gameObjects = new GameObject[]! [ new Player(), new Target(Direction.Up, 0, 0)];The second bad thing is, they tend to generate static arrays. So often you need to append a [] to convert the static array into a dynamic one. When generating D code, i use array initialization and cast every member to the type of the array element and append [] to every such initializer. This code looks really ugly. W Please rethink this syntax :)My thought is that the programmer should have the choice of implicitly-typed or explicitly-typed array literals. And that implicitly-typed array literals should be simultaneously of every type to which every element is implicitly convertible, in much the same way as string literals are simultaneously of types char[], wchar[] and dchar[]. And be simultaneously of static and dynamic array types. So for example, [ 42, 0, 6789 ] would be of the following types: short[3] short[] ushort[3] ushort[] int[3] int[] uint[3] uint[] long[3] long[] ulong[3] ulong[] and that's before you count the floating-point and complex versions....Or did I really missed the "good way of array initialization"?Pardon? Stewart. -- -----BEGIN GEEK CODE BLOCK----- Version: 3.1 GCS/M d- s:- C++ a->--- UB P+ L E W++ N+++ o K- w++ O? M V? PS- PE- Y? PGP- t- 5? X? R b DI? D G e++++ h-- r-- !y ------END GEEK CODE BLOCK------ My e-mail is valid but not my primary mailbox. Please keep replies on the 'group where everyone may benefit.
Nov 04 2006