On Sun, Feb 15, 2015 at 8:17 AM, Yasuo Ohgaki <yohg...@ohgaki.net> wrote:
> I wrote simple D program "sample.d" to play with. Install D, then
>
> dmd sample.d && ./sample
>
> ====sample.d====
> import std.stdio;
>
> class A {
> int x = 1;
> int y = 2;
>
> public:
> void set (int x, int y)
> in {
> assert(x > 0);
> assert(y > 0);
> }
> body {
> this.x = x;
> this.y = y;
> }
> int mul()
> out (ret) {
> assert(ret > 0);
> }
> body {
> return x * y;
> }
>
> invariant {
> assert(this.x > 0);
> assert(this.y > 0);
> }
> }
>
> class B : A {
> int a;
> int b;
> override void set (int a, int b)
> in {
> assert(a > 4);
> assert(b > 2);
> }
> body {
> this.a = a;
> this.b = b;
> }
> override int mul()
> out (ret) {
> assert(ret > 4);
> }
> body {
> return a * b;
> }
>
> invariant {
> assert(this.x > 0);
> assert(this.y > 0);
> }
> }
>
> class C : A {
> override void set (int x, int y)
> in {
> // Cannot work with override
> assert(x > -4);
> assert(y > -2);
> }
> body {
> this.x = x;
> this.y = y;
> }
> override int mul()
> out (ret) {
> assert(ret > -4);
> }
> body {
> return x * y;
> }
>
> // This cannot work. Less restrictive than parent
> invariant {
> assert(this.x > -4);
> assert(this.y > -2);
> }
> }
>
>
> void main()
> {
> A a = new A;
> B b = new B;
> C c = new C;
> a.set(4,2);
> writeln("Ans: ", a.mul());
> // -1 is invalid
> //a.set(-1, 0); core.exception.AssertError@sample.d(10): Assertion failure
>
> b.set(5,3); // Fine with B. B is different type.
> writeln("Ans: ", b.mul());
> }
> =================
>
>
> As you can see, D has type safety by contracts and does non-intuitive
> checks.
> Question is "Does PHP need this kind of type safety?"
>
> I totally agree strict type safety is good for writing correct programs,
> BTW.
> D has type safety feature since it has strong type. If PHP is going to be
> strongly typed language as scalar type hint RFC, and might be stronger
> type than now. We may consider stricter types later. It's not just time
> for it. IMHO.
> PHP may be extended to check contracts like D when
> declare('strict_types'=1).
>
I used latest D rpm package for CentOS/Fedore x86_64 from
http://dlang.org/download.html
It seems invariant() is removed from latest D, but the package can use
invariant().
You may get errors if you use real latest D.
Regards,
--
Yasuo Ohgaki
yohg...@ohgaki.net
