Fundamental Types

This lesson explores in detail the fundamental types we have in D language and their properties.

We'll cover the following

The need for a data type #

The smallest unit of data in a computer is called a bit. The value of a bit can be either 0 or 1. Since a type of data that can hold only the values 0 and 1 would have very limited use, the CPU supports larger data types that are combinations of more than one bit. As an example, a byte usually consists of 8 bits. If an N-bit data type is the most efficient data type supported by a CPU, we consider it to be an N-bit CPU: as in 32-bit CPU, 64-bit CPU, etc.

The data types that the CPU supports are still not sufficient because they can’t represent higher-level concepts like the name of a student or a playing card. Likewise, D’s fundamental data types are not sufficient to represent many higher-level concepts because of the various requirements like memory, specific operations, etc. Such concepts must be defined by the programmer as structs and classes.

D’s fundamental types #

D is statically typed, meaning every expression has a type. D’s fundamental types are very similar to the fundamental types of many other languages, as seen in the following table.

D's fundamental data types
D's fundamental data types

Note: In addition to the above, the keyword void represents having no type. The keywords cent and ucent are reserved for future use to represent signed and unsigned 128-bit values.

Whole numbers can be represented by int. To represent concepts that can have fractional values, consider double.

The following terms appear in the table above:

  • Boolean: The type of logical expressions that has the value true for truth and false for falsity.

  • Signed type: A type that can have both negative and positive values. For example, a byte can have values from -128 to 127. The names of the signed types come from the negative sign.

  • Unsigned type: A type that can have only positive values. For example, ubyte can have values from 0 to 255. The “u” at the beginning of the name of these types comes from unsigned.

  • Floating point: The type that can represent values with decimal points as in 1.25. The precision of floating point calculations is directly related to the bit count of the type: the higher the bit count, the more precise the results are. Only floating point types can represent fractions; integer types like int can only represent whole values like 1 and 2.

  • Complex number type: A type that can represent the complex numbers of mathematics having the form “a + bi”.

  • Imaginary number type: The type that represents only the imaginary part of complex numbers. The “i” that appears against this type in the “Initial Value” column of the table is called iota, which is equal to the square root of -1 in mathematics.

  • NaN: Short for “not a number,” represents an invalid floating- point value.

Properties of types #

D types have properties. Properties are accessed with a dot after the name of the type. For example, the sizeof property of int is accessed as int.sizeof. We will explore some of the properties of types in this chapter:

  • .stringof is the name of the type.

  • .sizeof is the length of the type in terms of bytes. (In order to determine the bit count, this value must be multiplied by 8, the number of bits in a byte.)

  • .min is short for “minimum”; this is the smallest value that the type can have.

  • .max is short for “maximum”; this is the largest value that the type can have.

  • .init is short for “initial value” (default value); this is the value that D assigns to a type when an initial value is not specified.

Example: int #

As an example, let’s explore the properties of type int.

Properties of int
Properties of int

Here is a program that displays these properties for int:

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import std.stdio;
void main() {
    writeln("Length in bytes: ", int.sizeof); 
    writeln("Minimum value : ", int.min); 
    writeln("Maximum value : ", int.max); 
    writeln("Initial value : ", int.init);
}

size_t #

You will occasionally come across the size_t type, as well. size_t is not a separate type but an alias of an existing unsigned type. Its name comes from “size type.” It is the most suitable type to represent concepts like the size of variables or count of array elements etc.

size_t is large enough to represent the number of bytes of memory that a program can potentially use. Its actual size depends on the system: uint on a 32-bit system and ulong on a 64-bit system. For this reason, ulong is larger than size_t on a 32-bit system.

You can use the .stringof property to see what size_t is an alias of on your system.

Note: You can’t use the reserved types cent and ucent in any program, and as an exception, void does not have the properties .min, .max and .init.
Additionally, the .min property is deprecated for floating point types. If you use a floating point type, you would be warned by the compiler that .min is not valid for that type. Instead, as we will see later in the floating point types lesson, you must use the negative of the .max property e.g., as -double.max.

Quick quiz! #

Try using data types in the code provided earlier in this lesson and then attempt the following quiz.

1

The length in bytes of char ____.

A)

1

B)

2

C)

3

D)

4

Question 1 of 50 attempted

In the next lesson, we will see how to assign values to variables.