Nullable

Defines a value paired with a distinctive "null" state that denotes the absence of a value. If default constructed, a Nullable!T object starts in the null state. Assigning it renders it non-null. Calling nullify can nullify it again. Practically Nullable!T stores a T and a bool.

struct Nullable (

) {

this(T value);

this(N n);

template toString();

bool isNull [@property getter];

static if(!is(T == immutable(T)) && !is(T == const(T)))

void opAssign(T value);

static if(!is(T == immutable(T)) && !is(T == const(T)))

void opAssign(N n);

static if(!is(T == immutable(T)) && !is(T == const(T)))

void nullify();

static if(__traits(compiles, (T a, T b)) && !is(T == class))

bool opEquals(N n);

static if(__traits(compiles, (T a, T b)) && !is(T == class))

bool opEquals(T rhs);

static if(__traits(compiles, (T a, T b)) && !is(T == class))

bool opEquals(Nullable!T rhs);

static if(__traits(compiles, (T a, T b)) && !is(T == class))

int opCmp(N n);

static if(__traits(compiles, (T a, T b)) && !is(T == class))

int opCmp(T rhs);

static if(__traits(compiles, (T a, T b)) && !is(T == class))

int opCmp(Nullable!T rhs);

inout(T) get [@property getter];

inout(T) getValueOr(T defVal);

}

Constructors

this this(T value): Constructor initializing this with value.
this this(N n): Undocumented in source.

Alias This

get

Implicitly converts to T. this must not be in the null state.

Members

Functions

getValueOr inout(T) getValueOr(T defVal): Gets the value or the default value passed in.
nullify void nullify(): Forces this to the null state.
opAssign void opAssign(T value)
void opAssign(N n): Assigns value to the internally-held state. If the assignment succeeds, this becomes non-null.
opCmp int opCmp(N n): Undocumented in source. Be warned that the author may not have intended to support it.
opCmp int opCmp(Nullable!T rhs): Undocumented in source. Be warned that the author may not have intended to support it.
opCmp int opCmp(T rhs): Undocumented in source. Be warned that the author may not have intended to support it.
opEquals bool opEquals(N n): Undocumented in source. Be warned that the author may not have intended to support it.
opEquals bool opEquals(T rhs): Undocumented in source. Be warned that the author may not have intended to support it.
opEquals bool opEquals(Nullable!T rhs): Undocumented in source. Be warned that the author may not have intended to support it.

Properties

get inout(T) get [@property getter]: Gets the value. this must not be in the null state. This function is also called for the implicit conversion to T.
isNull bool isNull [@property getter]: Check if this is in the null state.

Templates

toString template toString(): Undocumented in source.

Examples

struct CustomerRecord
{
    string name;
    string address;
    int customerNum;
}

Nullable!CustomerRecord getByName(string name)
{
    //A bunch of hairy stuff

    return Nullable!CustomerRecord.init;
}

auto queryResult = getByName("Doe, John");
if (!queryResult.isNull)
{
    //Process Mr. Doe's customer record
    auto address = queryResult.address;
    auto customerNum = queryResult.customerNum;

    //Do some things with this customer's info
}
else
{
    //Add the customer to the database
}

Nullable

Constructors

Alias This

Members

Functions

Properties

Templates

Examples

See Also

Meta

Source