Polia
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].
Exercise
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.
In-depth
