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version 2.109.1

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Alias std.traits.getSymbolsByUDA

alias getSymbolsByUDA(alias symbol, alias attribute) = AliasSeq!(symbol,membersWithUDA);

Parameters

NameDescription
symbol The aggregate type or module to search
attribute The user-defined attribute to search for

Returns

All symbols within symbol that have the given UDA attribute.

Note

This is not recursive; it will not search for symbols within symbols such as nested structs or unions.

Example

enum Attr;
struct A
{
    @Attr int a;
    int b;
}

static assert(getSymbolsByUDA!(A, Attr).length == 1);
static assert(hasUDA!(getSymbolsByUDA!(A, Attr)[0], Attr));

Example

enum Attr;

static struct A
{
    @Attr int a;
    int b;
    @Attr void doStuff() {}
    void doOtherStuff() {}
    static struct Inner
    {
        // Not found by getSymbolsByUDA
        @Attr int c;
    }
}

// Finds both variables and functions with the attribute, but
// doesn't include the variables and functions without it.
static assert(getSymbolsByUDA!(A, Attr).length == 2);
// Can access attributes on the symbols returned by getSymbolsByUDA.
static assert(hasUDA!(getSymbolsByUDA!(A, Attr)[0], Attr));
static assert(hasUDA!(getSymbolsByUDA!(A, Attr)[1], Attr));

Example

Finds multiple attributes 

static struct UDA { string name; }

static struct B
{
    @UDA("X")
    int x;
    @UDA("Y")
    int y;
    @(100)
    int z;
}

// Finds both UDA attributes.
static assert(getSymbolsByUDA!(B, UDA).length == 2);
// Finds one `100` attribute.
static assert(getSymbolsByUDA!(B, 100).length == 1);
// Can get the value of the UDA from the return value
static assert(getUDAs!(getSymbolsByUDA!(B, UDA)[0], UDA)[0].name == "X");

Example

Checks for UDAs on the aggregate symbol itself 

static struct UDA { string name; }

@UDA("A")
static struct C
{
    @UDA("B")
    int d;
}

static assert(getSymbolsByUDA!(C, UDA).length == 2);
static assert(getSymbolsByUDA!(C, UDA)[0].stringof == "C");
static assert(getSymbolsByUDA!(C, UDA)[1].stringof == "d");

Example

Finds nothing if there is no member with specific UDA 

static struct UDA { string name; }

static struct D
{
    int x;
}

static assert(getSymbolsByUDA!(D, UDA).length == 0);

Authors

Walter Bright, Tomasz Stachowiak (isExpressions), Andrei Alexandrescu, Shin Fujishiro, Robert Clipsham, David Nadlinger, Kenji Hara, Shoichi Kato

License

Boost License 1.0.