新コンパイルタイム・ポリモーフィズム(Metafunctionが要らない場合)

C++ Grammar
  • 結局、Metafunctionが要る場合と要らない場合に分かれるのではないかと思う
  • まずMetafunctionが要らない場合
    • メンバとADLを使ったカスタマイズを利用
    • tag dispatchと同じことはenable_ifで代用(overload型の存在価値が決定的に)
    • 継承階層を利用したい場合は、overloadを使って大域名前空間に定義する(継承は名前空間を越えられるから自然だ!?)
    • 大域名前空間に定義したものより、自分の名前空間の物の方が優先される (D型の場合)

[]namespace[] []pstade[][] {[]


[]class[] []hello_access[]

[]{[]

[]public[][]:[]

    []template[][]< [][]class[] []T[][] > [][]static[]

    []void[] []detail_call[][]([][]T[][]& [][]x[][])[]

[]    {[]

        []return[] []x[][].[][]pstade_hello[][]();[]

[]    }[]

[]};[]



[]namespace[] []hello_detail[][] {[]



    []PSTADE_HAS_XXX[][]([][]pstade_helloable[][])[]



    []struct[] []member_function[]

[]    {[]

        []template[][]< [][]class[] []T[][] > [][]static[]

        []void[] []call[][]([][]T[][]& [][]x[][])[]

[]        {[]

            []return[] []hello_access[][]::[][]detail_call[][]([][]x[][]);[]

[]        }[]

[]    };[]



    []template[][]< [][]class[] []T[][] > [][]inline[]

    []void[] []pstade_hello[][]([][]T[][]& [][]x[][])[]

[]    {[]

        []pstade_hello[][]([][]x[][], [][]pstade[][]::[][]overload[][]());[]

[]    }[]
    []struct[] []adl_customization[]

[]    {[]

        []template[][]< [][]class[] []T[][] > [][]static[]

        []void[] []call[][]([][]T[][]& [][]x[][])[]

[]        {[]

            []return[] []pstade_hello[][]([][]x[][]);[]

[]        }[]

[]    };[]



[]} [][]// namespace hello_detail[]



[]template[][]< [][]class[] []Helloable[][] > [][]inline[]

[]void[] []hello[][]([][]Helloable[][]& [][]h[][])[]

[]{[]

    []typedef[] []typename[]

    []boost[][]::[][]mpl[][]::[][]if_[][]< [][]hello_detail[][]::[][]has_pstade_helloable[][]<[][]Helloable[][]>,[]

        []hello_detail[][]::[][]member_function[][],[]

        []hello_detail[][]::[][]adl_customization[]

[]    >::[][]type[] []impl_t[][];[]
    []return[] []impl_t[][]::[][]call[][]([][]h[][]);[]

[]}[]



[]} [][]// namespace pstade[]



[]// user customizations[]

[]//[]
[]// intrusive way[]

[]//[]

[]struct[] []X[]

[]{[]

    []typedef[] []X[] []pstade_helloable[][];[]
[]private[][]:[]

    []friend[] []class[] []pstade[][]::[][]hello_access[][];[]
    []void[] []pstade_hello[][]()[]

[]    {[]

        []std[][]::[][]cout[][] << [][]"X\n"[][];[]

[]    }[]

[]};[]
[]// class hierarchy[]

[]//[]

[]struct[] []Base[][] { };[]

[]struct[] []Derived[][] : [][]Base[][] { };[]
[]inline[] []void[] []pstade_hello[][]([][]Base[][]&, [][]pstade[][]::[][]overload[][])[]

[]{[]

    []std[][]::[][]cout[][] << [][]"Base or Derived\n"[][];[]

[]};[]
[]// type set[]

[]//[]

[]struct[] []A[][] { };[]

[]namespace[] []Bs[][] { [][]struct[] []B[][] { }; }[]

[]struct[] []C[][] { };[]

[]namespace[] []Ds[]

[]{[]

    []struct[] []D[][] { };[]
    []inline[] []void[] []pstade_hello[][]([][]D[][]& [][]d[][])[]

[]    {[]

        []std[][]::[][]cout[][] << [][]"D\n"[][];[]

[]    }[]

[]}[]
[]template[][]< [][]class[] []T[][] >[]

[]struct[] []is_ABCD[][] :[]

    []boost[][]::[][]mpl[][]::[][]or_[][]<[]

        []boost[][]::[][]is_same[][]<[][]T[][], [][]A[][]>,[]

        []boost[][]::[][]is_same[][]<[][]T[][], [][]Bs[][]::[][]B[][]>,[]

        []boost[][]::[][]is_same[][]<[][]T[][], [][]C[][]>,[]

        []boost[][]::[][]is_same[][]<[][]T[][], [][]Ds[][]::[][]D[][]>[]

[]    >[]

[]{ };[]
[]template[][]< [][]class[] []T[][] >[]

[]typename[] []boost[][]::[][]enable_if[][]< [][]is_ABCD[][]<[][]T[][]>, [][]void[][] >::[][]type[]

[]pstade_hello[][]([][]T[][]& [][]x[][], [][]pstade[][]::[][]overload[][])[]

[]{[]

    []std[][]::[][]cout[][] << [][]"A, B, C, or D\n"[][];[]

[]}[]
[]inline[] []void[] []pstade_hello[][]([][]A[][]& [][]a[][], [][]pstade[][]::[][]overload[][])[]

[]{[]

    []std[][]::[][]cout[][] << [][]"A\n"[][];[]

[]}[]



[]void[] []test[][]()[]

[]{[]

    []X[] []x[][];[]

    []Base[] []base[][];[]

    []Derived[] []derived[][];[]

    []A[] []a[][];[]

    []Bs[][]::[][]B[] []b[][];[]

    []C[] []c[][];[]

    []Ds[][]::[][]D[] []d[][];[]
    []pstade[][]::[][]hello[][]([][]x[][]);           [][]// X[]

    []pstade[][]::[][]hello[][]([][]base[][]);        [][]// Base or Derived[]

    []pstade[][]::[][]hello[][]([][]derived[][]);     [][]// Base or Derived[]

    []pstade[][]::[][]hello[][]([][]a[][]);           [][]// A[]

    []pstade[][]::[][]hello[][]([][]b[][]);           [][]// A, B, C, or D[]

    []pstade[][]::[][]hello[][]([][]c[][]);           [][]// A, B, C, or D[]

    []pstade[][]::[][]hello[][]([][]d[][]);           [][]// D[]

[]}[]