Types - D Programming Language (original) (raw)

Contents

Grammar
Basic Data Types
Derived Data Types
1. Pointers
User-Defined Types
Type Conversions
bool
Function Types
1. Delegates
typeof
Mixin Types
Aliased Types
size_t
ptrdiff_t
string
noreturn

Grammar

D is statically typed. Every expression has a type. Types constrain the values an expression can hold, and determine the semantics of operations on those values.

Type: TypeCtorsopt BasicType TypeSuffixesopt

TypeCtors: TypeCtor TypeCtor TypeCtors

TypeCtor: const immutable inout shared

BasicType: FundamentalType . QualifiedIdentifier QualifiedIdentifier Typeof Typeof . QualifiedIdentifier TypeCtor ( Type ) Vector TraitsExpression MixinType

Vector: __vector ( VectorBaseType )

VectorBaseType: Type

FundamentalType: bool byte ubyte short ushort int uint long ulong cent ucent char wchar dchar float double real ifloat idouble ireal cfloat cdouble creal void

TypeSuffixes: TypeSuffix _TypeSuffixes_opt

TypeSuffix: * [ ] [ AssignExpression ] [ AssignExpression .. AssignExpression ] [ Type ] delegate Parameters MemberFunctionAttributesopt function Parameters FunctionAttributesopt

QualifiedIdentifier: Identifier Identifier . QualifiedIdentifier TemplateInstance TemplateInstance . QualifiedIdentifier Identifier [ AssignExpression ] Identifier [ AssignExpression ] . QualifiedIdentifier

Basic Data Types are leaf types.
Derived Data Types build on leaf types.
User-Defined Types are aggregates of basic and derived types.

Basic Data Types

Basic Data Types

Keyword	Default Initializer (.init)	Description
void	no default initializer	void has no value
bool	false	boolean value
byte	0	signed 8 bits
ubyte	0u	unsigned 8 bits
short	0	signed 16 bits
ushort	0u	unsigned 16 bits
int	0	signed 32 bits
uint	0u	unsigned 32 bits
long	0L	signed 64 bits
ulong	0uL	unsigned 64 bits
~~cent~~	0	signed 128 bits
~~ucent~~	0u	unsigned 128 bits
float	float.nan	32 bit floating point
double	double.nan	64 bit floating point
real	real.nan	largest floating point size available
ifloat	float.nan*1.0i	imaginary float
idouble	double.nan*1.0i	imaginary double
ireal	real.nan*1.0i	imaginary real
cfloat	float.nan+float.nan*1.0i	a complex number of two float values
cdouble	double.nan+double.nan*1.0i	complex double
creal	real.nan+real.nan*1.0i	complex real
char	'\xFF'	unsigned 8 bit (UTF-8 code unit)
wchar	'\uFFFF'	unsigned 16 bit (UTF-16 code unit)
dchar	'\U0000FFFF'	unsigned 32 bit (UTF-32 code unit)

Endianness of basic types is part of the ABI

Implementation Defined: The real floating point type has at least the range and precision of the double type. On x86 CPUs it is often implemented as the 80 bit Extended Real type supported by the x86 FPU.

NOTE: Complex and imaginary types ifloat, idouble, ireal, cfloat, cdouble, and creal have been deprecated in favor of std.complex.Complex.

Derived Data Types

int* p; int[2] sa; int[] da; int[string] aa; void function() fp; import std.meta : AliasSeq; AliasSeq!(int, string) tsi;

Pointers

A pointer to type T has a value which is a reference (address) to another object of type T. It is commonly called a pointer to T and its type isT*. To access the object value, use the * dereference operator:

int* p;

assert(p == null); p = new int(5); assert(p != null);

assert(*p == 5); (*p)++; assert(*p == 6);

If a pointer contains a null value, it is not pointing to a valid object.

When a pointer to T is dereferenced, it must either contain a null value, or point to a valid object of type T.

Implementation Defined:

The behavior when a null pointer is dereferenced. Typically the program will be aborted.

Undefined Behavior: dereferencing a pointer that is not null and does not point to a valid object of type T.

To set a pointer to point at an existing object, use the& address of operator:

int i = 2; int* p = &i;

assert(p == &i); assert(*p == 2); *p = 4; assert(i == 4);

User-Defined Types

Type Conversions

Pointer Conversions

Pointers implicitly convert to void*.

Casting between pointers and non-pointers is allowed. Some pointer casts are disallowed in @safe code.

Best Practices: do not cast any pointer to a non-pointer type that points to data allocated by the garbage collector.

Implicit Conversions

Implicit conversions are used to automatically convert types as required. The rules for integers are detailed in the next sections.

An enum can be implicitly converted to its base type, but going the other way requires an explicit conversion.

All types implicitly convert to noreturn.
Static and dynamic arrays implicitly convert to void arrays.
Function pointers and delegates can convert to covariant types.

Class Conversions

A derived class can be implicitly converted to its base class, but going the other way requires an explicit cast. For example:

class Base {} class Derived : Base {} Base bd = new Derived(); Derived db = cast(Derived)new Base();

A dynamic array, say x, of a derived class can be implicitly converted to a dynamic array, say y, of a base class iff elements of x and y are qualified as being either both const or both immutable.

class Base {} class Derived : Base {} const(Base)[] ca = (const(Derived)[]).init; immutable(Base)[] ia = (immutable(Derived)[]).init;

A static array, say x, of a derived class can be implicitly converted to a static array, say y, of a base class iff elements of x and y are qualified as being either both const or both immutable or both mutable (neither const nor immutable).

class Base {} class Derived : Base {} Base[3] ma = (Derived[3]).init; const(Base)[3] ca = (const(Derived)[3]).init; immutable(Base)[3] ia = (immutable(Derived)[3]).init;

Integer Promotions

Integer Promotions are conversions of the following types:

Integer Promotions

from	to
bool	int
byte	int
ubyte	int
short	int
ushort	int
char	int
wchar	int
dchar	uint

If an enum has as a base type one of the types in the left column, it is converted to the type in the right column.

Integer promotion applies to each operand of a binary expression:

void fun() { byte a; auto b = a + a; static assert(is(typeof(b) == int));

ushort d;
        int e = d * d;     static assert(is(typeof(int() * d) == int));

dchar f;
static assert(is(typeof(f - f) == uint));

}

Rationale:

32-bit integer operations are often faster than smaller integer types for single variables on modern architectures.
Promotion helps avoid accidental overflow which is more common with small integer types.

Usual Arithmetic Conversions

The usual arithmetic conversions convert operands of binary operators to a common type. The operands must already be of arithmetic types. The following rules are applied in order, looking at the base type:

If either operand is real, the other operand is converted to real.
Else if either operand is double, the other operand is converted to double.
Else if either operand is float, the other operand is converted to float.
Else the integer promotions above are done on each operand, followed by:
1. If both are the same type, no more conversions are done.
2. If both are signed or both are unsigned, the smaller type is converted to the larger.
3. If the signed type is larger than the unsigned type, the unsigned type is converted to the signed type.
4. The signed type is converted to the unsigned type.

Rationale: The above rules follow C99, which makes porting code from C easier.

Example: Signed and unsigned conversions:

int i; uint u; static assert(is(typeof(i + u) == uint)); static assert(is(typeof(short() + u) == uint)); static assert(is(typeof(ulong() + i) == ulong)); static assert(is(typeof(long() - u) == long)); static assert(is(typeof(long() * ulong()) == ulong));

Example: Floating point:

float f; static assert(is(typeof(f + ulong()) == float));

double d; static assert(is(typeof(f * d) == double)); static assert(is(typeof(real() / d) == real));

Enum Operations

If one or both of the operand types is an enum after undergoing the above conversions, the result type is determined as follows:

If the operands are the same type, the result will be of that type.
If one operand is an enum and the other is the base type of that enum, the result is the base type.
If the two operands are different enums, the result is the closest base type common to both. A base type being closer means there is a shorter sequence of conversions to base type to get there from the original type.

enum E { a, b, c } enum F { x, y }

void test() { E e = E.a; e = e | E.c; int i = e + 4; e += 4; F f; i = e | f; }

Note: Above, e += 4 compiles because theoperator assignment is equivalent to e = cast(E)(e + 4).

Integer Type Conversions

An integer of type I implicitly converts to another integer type J whenJ.sizeof >= I.sizeof.

void f(byte b, ubyte ub, short s) { b = ub; ub = b; s = b; b = s; }

Integer values cannot be implicitly converted to another type that cannot represent the integer bit pattern afterintegral promotion. For example:

ubyte u1 = -1; ushort u2 = -1; uint u3 = -1; ulong u4 = -1;

Floating Point Type Conversions

Integral types implicitly convert to floating point types.
Floating point types cannot be implicitly converted to integral types.

void f(int i, float f) { f = i; i = f; }

Complex or imaginary floating point types cannot be implicitly converted to non-complex floating point types.
Non-complex floating point types cannot be implicitly converted to imaginary floating point types.

Value Range Propagation

Besides type-based implicit conversions, D allows certain integer expressions to implicitly convert to a narrower type after integer promotion. This works by analysing the minimum and maximum possible range of values for each expression. If that range of values matches or is a subset of a narrower target type's value range, implicit conversion is allowed. If a subexpression is known at compile-time, that can further narrow the range of values.

void fun(char c, int i, ubyte b) { short s = c + 100; ubyte j = i & 0x3F; ushort k = i & 0x14A; k = i & b; s = b + b; }

Note the implementation does not track the range of possible values for mutable variables:

void fun(int i) { ushort s = i & 0xff; ubyte b = s & 0xff; const int c = i & 0xff; b = c; }

For more information, see the dmc article.
See also: https://en.wikipedia.org/wiki/Value_range_analysis.

bool

The bool type is a byte-size type that can only hold the value true orfalse.

The only operators that can accept operands of type bool are: & |, ^, &=, |=, ^=, !,&&, ||, and ?:.

A bool value can be implicitly converted to any integral type, withfalse becoming 0 and true becoming 1.

The numeric literals 0 and 1 can be implicitly converted to the boolvalues false and true, respectively. Casting an expression to bool means testing !=0 for arithmetic types, and !=null for pointers or references.

Undefined Behavior:

Interpreting a value with a byte representation other than 0 or 1 as bool (e.g. an overlapped union field).
Reading a void-initialized bool.

byte i = 2; bool b = cast(bool) i; assert(b);

bool* p = cast(bool*) &i;

Function Types

A function type has the form:

StorageClassesopt Type Parameters FunctionAttributesopt

Function types are not included in the Type grammar. A function type e.g. int(int) can be aliased. A function type is only used for type tests or as the target type of a pointer.

Instantiating a function type is illegal. Instead, a pointer to function or delegate can be used. Those have these type forms respectively:

Type function Parameters FunctionAttributesopt Type delegate Parameters MemberFunctionAttributesopt

void f(int); alias Fun = void(int); static assert(is(typeof(f) == Fun)); static assert(is(Fun* == void function(int)));

See Function Pointers.

Delegates

Delegates are an aggregate of two pieces of data, either:

An object reference and a pointer to a non-staticmember function.
A pointer to a closure and a pointer to anested function. The object reference forms the this pointer when the function is called.

Delegates are declared and initialized similarly to function pointers:

int delegate(int) dg; class OB { int member(int); }

void f(OB o) { dg = &o.member; }

Delegates cannot be initialized with static member functions or non-member functions.

Delegates are called analogously to function pointers:

fp(3); dg(3);

The equivalent of member function pointers can be constructed using anonymous lambda functions:

class C { int a; int foo(int i) { return i + a; } }

auto mfp = function(C self, int i) { return self.foo(i); }; auto c = new C(); mfp(c, 1);

typeof

Typeof: typeof ( Expression ) typeof ( return )

typeof is a way to specify a type based on the type of an expression. For example:

void func(int i) { typeof(i) j; typeof(3 + 6.0) x; typeof(1)* p; int[typeof(p)] a;
writeln(typeof('c').sizeof); double c = cast(typeof(1.0))j; }

Expression is not evaluated, it is used purely to generate the type:

void func() { int i = 1; typeof(++i) j; writeln(i); }

If Expression is aValueSeq it will produce a TypeSeq containing the types of each element.

Special cases:

typeof(return) will, when inside a function scope, give the return type of that function.
typeof(this) will generate the type of what this would be in a non-static member function, even if not in a member function.
Analogously, typeof(super) will generate the type of whatsuper would be in a non-static member function.

class A { }

class B : A { typeof(this) x; typeof(super) y; }

struct C { static typeof(this) z;
typeof(super) q; }

typeof(this) r;

If the expression is a Property Function, typeof gives its return type.

struct S { @property int foo() { return 1; } } typeof(S.foo) n;

If the expression is a Template,typeof gives the type void.

template t {} static assert(is(typeof(t) == void));

Best Practices:

Typeof is most useful in writing generic template code.

Mixin Types

MixinType: mixin ( ArgumentList )

Each AssignExpression in the ArgumentList is evaluated at compile time, and the result must be representable as a string. The resulting strings are concatenated to form a string. The text contents of the string must be compilable as a validType, and is compiled as such.

void test(mixin("int")* p) { mixin("int")[] a; mixin("int[]") b; }

noreturn abort(const(char)[] message);

int example(int i) { if (i < 0) { int val = abort("less than zero"); } return i != 0 ? 1024 / i : abort("calculation went awry."); }

noreturn is defined as typeof(*null). This is because dereferencing a null literal halts execution.

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