There are two types of Arrays in D: static and dynamic. Access to arrays of any kind is bounds-checked (except when the compiler can prove that bounds checks aren't necessary). A failed bounds check yields a RangeError which aborts the application. The brave can disable this safety feature with the compiler flag -boundschecks=off in order to gain speed improvements at the cost of safety.

Static arrays

Static arrays are stored on the stack if defined inside a function, or in static memory otherwise. They have a fixed, compile-time known length. A static array's type includes the fixed size:

int[8] arr;

arr's type is int[8]. Note that the size of the array is denoted next to the type, and not after the variable name like in C/C++.

Dynamic arrays

Dynamic arrays are stored on the heap and can be expanded or shrunk at runtime. A dynamic array is created using a new expression and its length:

int size = 8; // run-time variable
int[] arr = new int[size];

The type of arr is int[], which is a slice. Slices will be explained in more detail in the next section. Multi-dimensional arrays can be created easily using the auto arr = new int[3][3] syntax.

Array operations and properties

Arrays can be concatenated using the ~ operator, which will create a new dynamic array.

Mathematical operations can be applied to whole arrays using a syntax like c[] = a[] + b[], for example. This adds all elements of a and b so that c[0] = a[0] + b[0], c[1] = a[1] + b[1], etc. It is also possible to perform operations on a whole array with a single value:

a[] *= 2; // multiple all elements by 2
a[] %= 26; // calculate the modulo by 26 for all a's

These operations might be optimized by the compiler to use special processor instructions that do the operations in one go.

Both static and dynamic arrays provide the property .length, which is read-only for static arrays, but can be used in the case of dynamic arrays to change its size dynamically. The property .dup creates a copy of the array.

When indexing an array through the arr[idx] syntax, a special $ symbol denotes an array's length. For example, arr[$ - 1] references the last element and is a short form for arr[arr.length - 1].


Complete the function encrypt to decrypt the secret message. The text should be encrypted using Caesar encryption, which shifts the characters in the alphabet using a certain index. The to-be-encrypted text only contains characters in the range a-z, which should make things easier.


rdmd playground.d