@safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto w1 = appender!string();    auto spec1 = singleSpec("%s");    formatValue(w1, true, spec1);     assert(w1.data == "true");     auto w2 = appender!string();    auto spec2 = singleSpec("%#x");    formatValue(w2, true, spec2);     assert(w2.data == "0x1");} @safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto w = appender!string();    auto spec = singleSpec("%s");    formatValue(w, null, spec);     assert(w.data == "null");} @safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto w1 = appender!string();    auto spec1 = singleSpec("%d");    formatValue(w1, -1337, spec1);     assert(w1.data == "-1337");     auto w2 = appender!string();    auto spec2 = singleSpec("%x");    formatValue(w2, -1337, spec2);     assert(w2.data == "fffffac7");} @safe unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto w1 = appender!string();    auto spec1 = singleSpec("%.3f");    formatValue(w1, 1337.7779, spec1);     assert(w1.data == "1337.778");     auto w2 = appender!string();    auto spec2 = singleSpec("%.3e");    formatValue(w2, 1337.7779, spec2);     assert(w2.data == "1.338e+03");     auto w3 = appender!string();    auto spec3 = singleSpec("%.3g");    formatValue(w3, 1337.7779, spec3);     assert(w3.data == "1.34e+03");     auto w4 = appender!string();    auto spec4 = singleSpec("%.3a");    formatValue(w4, 1337.7779, spec4);     assert(w4.data == "0x1.4e7p+10");} @safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto w1 = appender!string();    auto spec1 = singleSpec("%c");    formatValue(w1, 'ì', spec1);     assert(w1.data == "ì");     auto w2 = appender!string();    auto spec2 = singleSpec("%#x");    formatValue(w2, 'ì', spec2);     assert(w2.data == "0xec");} @safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto w1 = appender!string();    auto spec1 = singleSpec("%s");    formatValue(w1, "hello", spec1);     assert(w1.data == "hello");     auto w2 = appender!string();    auto spec2 = singleSpec("%(%#x%|/%)");    formatValue(w2, "hello", spec2);     assert(w2.data == "0x68/0x65/0x6c/0x6c/0x6f");} @safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto w = appender!string();    auto spec = singleSpec("%s");    int[2] two = [1, 2];    formatValue(w, two, spec);     assert(w.data == "[1, 2]");} @safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto w1 = appender!string();    auto spec1 = singleSpec("%s");    auto two = [1, 2];    formatValue(w1, two, spec1);     assert(w1.data == "[1, 2]");     auto w2 = appender!string();    auto spec2 = singleSpec("%(%g%|, %)");    auto consts = [3.1415926, 299792458, 6.67430e-11];    formatValue(w2, consts, spec2);     assert(w2.data == "3.14159, 2.99792e+08, 6.6743e-11");     // void[] is treated like ubyte[]    auto w3 = appender!string();    auto spec3 = singleSpec("%s");    void[] val = cast(void[]) cast(ubyte[])[1, 2, 3];    formatValue(w3, val, spec3);     assert(w3.data == "[1, 2, 3]");} @safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto aa = [10:17.5, 20:9.99];     auto w1 = appender!string();    auto spec1 = singleSpec("%s");    formatValue(w1, aa, spec1);     assert(w1.data == "[10:17.5, 20:9.99]" || w1.data == "[20:9.99, 10:17.5]");     auto w2 = appender!string();    auto spec2 = singleSpec("%(%x = %.0e%| # %)");    formatValue(w2, aa, spec2);     assert(w2.data == "a = 2e+01 # 14 = 1e+01" || w2.data == "14 = 1e+01 # a = 2e+01");} @safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     enum A { first, second, third }     auto w1 = appender!string();    auto spec1 = singleSpec("%s");    formatValue(w1, A.second, spec1);     assert(w1.data == "second");     auto w2 = appender!string();    auto spec2 = singleSpec("%d");    formatValue(w2, A.second, spec2);     assert(w2.data == "1");     // values of an enum that have no name are formatted with %s using a cast    A a = A.third;    a++;     auto w3 = appender!string();    auto spec3 = singleSpec("%s");    formatValue(w3, a, spec3);     assert(w3.data == "cast(A)3");} @safe unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : FormatSpec, singleSpec;     // Using a `toString` with a writer    static struct Point1    {        import std.range.primitives : isOutputRange, put;         int x, y;         void toString(W)(ref W writer, scope const ref FormatSpec!char f)        if (isOutputRange!(W, char))        {            put(writer, "(");            formatValue(writer, x, f);            put(writer, ",");            formatValue(writer, y, f);            put(writer, ")");        }    }     auto w1 = appender!string();    auto spec1 = singleSpec("%s");    auto p1 = Point1(16, 11);     formatValue(w1, p1, spec1);    assert(w1.data == "(16,11)");     // Using a `toString` with a sink    static struct Point2    {        int x, y;         void toString(scope void delegate(scope const(char)[]) @safe sink,                      scope const FormatSpec!char fmt) const        {            sink("(");            sink.formatValue(x, fmt);            sink(",");            sink.formatValue(y, fmt);            sink(")");        }    }     auto w2 = appender!string();    auto spec2 = singleSpec("%03d");    auto p2 = Point2(16,11);     formatValue(w2, p2, spec2);    assert(w2.data == "(016,011)");     // Using `string toString()`    static struct Point3    {        int x, y;         string toString()        {            import std.conv : to;             return "(" ~ to!string(x) ~ "," ~ to!string(y) ~ ")";        }    }     auto w3 = appender!string();    auto spec3 = singleSpec("%s"); // has to be %s    auto p3 = Point3(16,11);     formatValue(w3, p3, spec3);    assert(w3.data == "(16,11)");     // without `toString`    static struct Point4    {        int x, y;    }     auto w4 = appender!string();    auto spec4 = singleSpec("%s"); // has to be %s    auto p4 = Point4(16,11);     formatValue(w4, p4, spec3);    assert(w4.data == "Point4(16, 11)");} @safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto w1 = appender!string();    auto spec1 = singleSpec("%s");    auto p1 = () @trusted { return cast(void*) 0xFFEECCAA; } ();    formatValue(w1, p1, spec1);     assert(w1.data == "FFEECCAA");     // null pointers are printed as `"null"` when used with `%s` and as hexadecimal integer else    auto w2 = appender!string();    auto spec2 = singleSpec("%s");    auto p2 = () @trusted { return cast(void*) 0x00000000; } ();    formatValue(w2, p2, spec2);     assert(w2.data == "null");     auto w3 = appender!string();    auto spec3 = singleSpec("%x");    formatValue(w3, p2, spec3);     assert(w3.data == "0");} @safe unittest{    import std.format.write;     import core.simd; // cannot be selective, because float4 might not be defined    import std.array : appender;    import std.format.spec : singleSpec;     auto w = appender!string();    auto spec = singleSpec("%s");     static if (is(float4))    {        version (X86) {}        else        {            float4 f4;            f4.array[0] = 1;            f4.array[1] = 2;            f4.array[2] = 3;            f4.array[3] = 4;             formatValue(w, f4, spec);            assert(w.data == "[1, 2, 3, 4]");        }    }} @safe pure unittest{    import std.format.write;     import std.array : appender;     auto writer1 = appender!string();    formattedWrite(writer1, "%s is the ultimate %s.", 42, "answer");    assert(writer1[] == "42 is the ultimate answer.");     auto writer2 = appender!string();    formattedWrite(writer2, "Increase: %7.2f %%", 17.4285);    assert(writer2[] == "Increase:   17.43 %");} @safe pure unittest{    import std.format.write;     import std.array : appender;     auto writer = appender!string();    writer.formattedWrite!"%d is the ultimate %s."(42, "answer");    assert(writer[] == "42 is the ultimate answer.");     // This line doesn't compile, because 3.14 cannot be formatted with %d:    // writer.formattedWrite!"%d is the ultimate %s."(3.14, "answer");} @safe pure unittest{    import std.format.write;     import std.array : appender;    import std.format.spec : singleSpec;     auto writer = appender!string();    auto spec = singleSpec("%08b");    writer.formatValue(42, spec);    assert(writer.data == "00101010");     spec = singleSpec("%2s");    writer.formatValue('=', spec);    assert(writer.data == "00101010 =");     spec = singleSpec("%+14.6e");    writer.formatValue(42.0, spec);    assert(writer.data == "00101010 = +4.200000e+01");}