gistfile1.d

/*
 * The term »template predicate« as used below refers to a eponymous template
 * which (typically) takes a single argument and evaluates to a bool constant.
 */

/**
 * Returns a type tuple containing only the elements of T for which the
 * eponymous template predicate pred is true.
 *
 * Example:
 * ---
 * alias StaticFilter!(isIntegral, int, string, long, float[]) Filtered;
 * static assert(is(Filtered == TypeTuple!(int, long)));
 * ---
 */
template StaticFilter(alias pred, T...) {
  static if (T.length == 0) {
    alias TypeTuple!() StaticFilter;
  } else static if (pred!(T[0])) {
    alias TypeTuple!(T[0], StaticFilter!(pred, T[1 .. $])) StaticFilter;
  } else {
    alias StaticFilter!(pred, T[1 .. $]) StaticFilter;
  }
}

/**
 * Binds the first n arguments of a template to a particular value (where n is
 * the number of arguments passed to PApply).
 *
 * The passed arguments are always applied starting from the left. However,
 * the special PApplySkip marker template can be used to indicate that an
 * argument should be skipped, so that e.g. the first and third argument
 * to a template can be fixed, but the second and remaining arguments would
 * still be left undefined.
 *
 * Skipping a number of parameters, but not providing enough arguments to
 * assign all of them during instantiation of the resulting template is an
 * error.
 *
 * Example:
 * ---
 * struct Foo(T, U, V) {}
 * alias PApply!(Foo, int, long) PartialFoo;
 * static assert(is(PartialFoo!float == Foo!(int, long, float)));
 *
 * alias PApply!(Test, int, PApplySkip, float) SkippedTest;
 * static assert(is(SkippedTest!long == Test!(int, long, float)));
 * ---
 */
template PApply(alias Target, T...) {
  template PApply(U...) {
    alias Target!(PApplyMergeArgs!(ConfinedTuple!T, U).Result) PApply;
  }
}

/// Ditto.
template PApplySkip() {}

private template PApplyMergeArgs(alias Preset, Args...) {
  static if (Preset.length == 0) {
    alias Args Result;
  } else {
    enum nextSkip = staticIndexOf!(PApplySkip, Preset.Tuple);
    static if (nextSkip == -1) {
      alias TypeTuple!(Preset.Tuple, Args) Result;
    } else static if (Args.length == 0) {
      // Have to use a static if clause instead of putting the condition
      // directly into the assert to avoid DMD trying to access Args[0]
      // nevertheless below.
      static assert(false,
        "PArgsSkip encountered, but no argument left to bind.");
    } else {
      alias TypeTuple!(
        Preset.Tuple[0 .. nextSkip],
        Args[0],
        PApplyMergeArgs!(
          ConfinedTuple!(Preset.Tuple[nextSkip + 1 .. $]),
          Args[1 .. $]
        ).Result
      ) Result;
    }
  }
}

/**
 * Composes a number of templates. The result is a template equivalent to
 * all the passed templates evaluated from right to left, akin to the
 * mathematical function composition notation: Instantiating Compose!(A, B, C)
 * is the same as instantiating A!(B!(C!(…))).
 *
 * This is especially useful for creating a template to use with staticMap/
 * StaticFilter, as demonstrated below.
 *
 * Example:
 * ---
 * template AllMethodNames(T) {
 *   alias StaticFilter!(
 *     CompilesAndTrue!(
 *       Compose!(isSomeFunction, GetType, PApply!(GetMember, T))
 *     ),
 *     __traits(allMembers, T)
 *   ) AllMethodNames;
 * }
 *
 * pragma(msg, AllMethodNames!Object);
 * ---
 */
template Compose(T...) {
  static if (T.length == 0) {
    template Compose(U...) {
      alias U Compose;
    }
  } else {
    template Compose(U...) {
      alias Instantiate!(T[0], Instantiate!(.Compose!(T[1 .. $]), U)) Compose;
    }
  }
}

/**
 * Instantiates the given template with the given list of parameters.
 *
 * Used to work around syntactic limiations of D with regard to instantiating
 * a template from a type tuple (e.g. T[0]!(...) is not valid) or a template
 * returning another template (e.g. Foo!(Bar)!(Baz) is not allowed).
 */
template Instantiate(alias Template, Params...) {
  alias Template!Params Instantiate;
}

/**
 * Combines several template predicates using logical AND, i.e. instantiating
 * All!(a, b, c) with parameters P for some templates a, b, c is equivalent to
 * a!P && b!P && c!P.
 *
 * The templates are evaluated from left to right, aborting evaluation in a
 * shurt-cut manner if a false result is encountered, in which case the latter
 * instantiations do not need to compile.
 */
template All(T...) {
  static if (T.length == 0) {
    template All(U...) {
      enum All = true;
    }
  } else {
    template All(U...) {
      static if (Instantiate!(T[0], U)) {
        alias Instantiate!(.All!(T[1 .. $]), U) All;
      } else {
        enum All = false;
      }
    }
  }
}

/**
 * Combines several template predicates using logical OR, i.e. instantiating
 * Any!(a, b, c) with parameters P for some templates a, b, c is equivalent to
 * a!P || b!P || c!P.
 *
 * The templates are evaluated from left to right, aborting evaluation in a
 * shurt-cut manner if a true result is encountered, in which case the latter
 * instantiations do not need to compile.
 */
template Any(T...) {
  static if (T.length == 0) {
    template Any(U...) {
      enum Any = false;
    }
  } else {
    template Any(U...) {
      static if (Instantiate!(T[0], U)) {
        enum Any = true;
      } else {
        alias Instantiate!(.Any!(T[1 .. $]), U) Any;
      }
    }
  }
}

/**
 * Negates the passed template predicate.
 */
template Not(alias T) {
  template Not(U...) {
    enum Not = !T!U;
  }
}

/**
 * Wraps the passed template predicate so it returns true if it compiles and
 * evaluates to true, false it it doesn't compile or evaluates to false.
 */
template CompilesAndTrue(alias T) {
  template CompilesAndTrue(U...) {
    static if (is(typeof(T!U) : bool)) {
      enum bool CompilesAndTrue = T!U;
    } else {
      enum bool CompilesAndTrue = false;
    }
  }
}

// Copyright: David Nadlinger
// License: Boost License 1.0 (http://www.boost.org/LICENSE_1_0.txt)