D Cookbook by 未知

Author:未知
Language: eng
Format: mobi
Publisher: Packt Publishing

Tip

When writing bindings to C libraries, import core.stdc.config; and use the types c_long and c_ulong to do the correct translation. However, while this issue can be fairly easily fixed, the static assert still serves as a valuable sanity check to ensure you did do this correctly and to be a first line of defense against other translation mistakes.

Checking structure sizes is not the only thing done by static assert. It can check anything that can be run at compile time. We've used it before to verify our range objects adhere to a particular compile-time interface. Phobos' std.random also uses it to ensure parameters to a random number engine are good for pseudorandom number generation by checking the greatest common denominator and number of factors the integer parameters have.

It achieves these checks by simply writing regular functions to check the numbers and calling them in a series of static assert statements in the object as shown as follows:

struct LinearCongruentialEngine(UIntType, UIntType a, UIntType c, UIntType m) { private static bool properLinearCongruentialParameters( ulong m, ulong a, ulong c) { /* snip some implementation */ if (a == 0 || a >= m || c >= m) return false; // c and m are relatively prime if (c > 0 && gcd(c, m) != 1) return false; // a - 1 is divisible by all prime factors of m if ((a - 1) % primeFactorsOnly(m)) return false; // if a - 1 is multiple of 4, then m is a multiple of 4 too. if ((a - 1) % 4 == 0 && m % 4) return false; // Passed all tests return true; } static assert(c == 0 || properLinearCongruentialParameters(m, a, c), "Incorrect instantiation of LinearCongruentialEngine"); /* Snip remaining object implementation */ }

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