int* p; Simple pointers to data int[3] s; Static arrays int[] a; Dynamic arrays int[char[]] x; Associative arrays (discussed later)
int* p;These are simple pointers to data, analogous to C pointers. Pointers are provided for interfacing with C and for specialized systems work. There is no length associated with it, and so there is no way for the compiler or runtime to do bounds checking, etc., on it. Most conventional uses for pointers can be replaced with dynamic arrays, out and inout parameters, and handles (references).
int[3] s;These are analogous to C arrays. Static arrays are distinguished by having a length fixed at compile time.
int[] a;Dynamic arrays contain a length and a garbage collected pointer to the array data.
int *[]*[3] p;declares p as an array of 3 pointers to dynamic arrays of pointers to ints.
The handle to an array is specified by naming the array, as in p, s or a:
int* p; int[3] s; int[] a; int* q; int[3] t; int[] b; p = q; p points to the same thing q does. p = s; p points to the first element of the array s. p = a; p points to the first element of the array a. s = ...; error, since s is a compiled in static reference to an array. a = p; error, since the length of the array pointed to by p is unknown a = s; a is initialized to point to the s array a = b; a points to the same array as b does
int a[10]; declare array of 10 ints int b[]; b = a[1..3]; a[1..3] is a 2 element array consisting of a[1] and a[2]The [] is shorthand for a slice of the entire array. For example, the assignments to b:
int a[10]; int b[] b = a; b = a[]; b = a[0 .. a.length];are all semantically equivalent.
Slicing is not only handy for referring to parts of other arrays, but for converting pointers into bounds-checked arrays:
int *p; int b[] = p[0..8];
int[3] s; int[3] t; s[] = t; the 3 elements of t[3] are copied into s[3] s[] = t[]; the 3 elements of t[3] are copied into s[3] s[1..2] = t[0..1]; same as s[1] = t[0] s[0..2] = t[1..3]; same as s[0] = t[1], s[1] = t[2] s[0..4] = t[0..4]; error, only 3 elements in s s[0..2] = t; error, different lengths for lvalue and rvalueOverlapping copies are an error:
s[0..2] = s[1..3]; error, overlapping copy s[1..3] = s[0..2]; error, overlapping copyDisallowing overlapping makes it possible for more aggressive parallel code optimizations than possible with the serial semantics of C.
int[3] s; int *p; s[] = 3; same as s[0] = 3, s[1] = 3, s[2] = 3 p[0..2] = 3; same as p[0] = 3, p[1] = 3
int a[]; int b[]; int c[]; a = b ~ c; Create an array from the concatenation of the b and c arraysMany languages overload the + operator to mean concatenation. This confusingly leads to, does:
"10" + 3produce the number 13 or the string "103" as the result? It isn't obvious, and the language designers wind up carefully writing rules to disambiguate it - rules that get incorrectly implemented, overlooked, forgotten, and ignored. It's much better to have + mean addition, and a separate operator to be array concatenation.
Similarly, the ~= operator means append, as in:
a ~= b; a becomes the concatenation of a and bConcatenation always creates a copy of its operands, even if one of the operands is a 0 length array, so:
a = b a refers to b a = b ~ c[0..0] a refers to a copy of b
for (i = n; i < m; i++) a[i] op e;So, for the expression:
a[] = b[] + 3;the result is equivalent to:
for (i = 0; i < a.length; i++) a[i] = b[i] + 3;When more than one [] operator appears in an expression, the range represented by all must match.
a[1..2] = b[] + 3; error, 2 elements not same as 3 elements
int[3] abc; // static array of 3 ints int[] def = { 1, 2, 3 }; // dynamic array of 3 ints void dibb(int *array) { array[2]; // means same thing as *(array + 2) *(array + 2); // get 2nd element } void diss(int[] array) { array[2]; // ok *(array + 2); // error, array is not a pointer } void ditt(int[3] array) { array[2]; // ok *(array + 2); // error, array is not a pointer }
double matrix[][];declares matrix as an array of pointers to arrays. (Dynamic arrays are implemented as pointers to the array data.) Since the arrays can have varying sizes (being dynamically sized), this is sometimes called "jagged" arrays. Even worse for optimizing the code, the array rows can sometimes point to each other! Fortunately, D static arrays, while using the same syntax, are implemented as a fixed rectangular layout:
double matrix[3][3];declares a rectangular matrix with 3 rows and 3 columns, all contiguously in memory. In other languages, this would be called a multidimensional array and be declared as:
double matrix[3,3];
length number of elements in the array p.length error, length not known for pointer s.length compile time constant 3 a.length runtime value dup create a dynamic array of the same size and copy the contents of the array into it p.dup error, length not known s.dup creates an array of 3 elements, copies elements s into it a.dup creates an array of a.length elements, copies elements of a into it
try { for (i = 0; ; i++) { array[i] = 5; } } catch (ArrayBoundsError) { // terminate loop }The loop is correctly written:
for (i = 0; i < array.length; i++) { array[i] = 5; }Implementation Note: Compilers should attempt to detect array bounds errors at compile time, for example:
int[3] foo; int x = foo[3]; // error, out of boundsInsertion of array bounds checking code at runtime should be turned on and off with a compile time switch.
int[3] a = [ 1:2, 3 ]; // a[0] = 0, a[1] = 2, a[2] = 3This is most handy when the array indices are given by enums:
enum Color { red, blue, green }; int value[Color.max] = [ blue:6, green:2, red:5 ];If any members of an array are initialized, they all must be. This is to catch common errors where another element is added to an enum, but one of the static instances of arrays of that enum was overlooked in updating the initializer list.
bit[10] x; // array of 10 bitsThe amount of storage used up is implementation dependent. Implementation Note: on Intel CPUs it would be rounded up to the next 32 bit size.
x.length // 10, number of bits x.size // 4, bytes of storageSo, the size per element is not (x.size / x.length).
Dynamic arrays in D suggest the obvious solution - a string is just a dynamic array of characters. String literals become just an easy way to write character arrays.
char[] str; char[] str1 = "abc";Strings can be copied, compared, concatenated, and appended:
str1 = str2; if (str1 < str3) ... func(str3 + str4); str4 += str1;with the obvious semantics. Any generated temporaries get cleaned up by the garbage collector (or by using alloca()). Not only that, this works with any array not just a special String array.
A pointer to a char can be generated:
char *p = &str[3]; // pointer to 4th element char *p = str; // pointer to 1st elementSince strings, however, are not 0 terminated in D, when transfering a pointer to a string to C, add a terminating 0:
str.append(0);The type of a string is determined by the semantic phase of compilation. The type is one of: ascii, wchar, ascii[], wchar[], and is determined by implicit conversion rules. If there are two equally applicable implicit conversions, the result is an error. To disambiguate these cases, a cast is approprate:
(wchar [])"abc" // this is an array of wchar charactersIt is an error to implicitly convert a string containing non-ascii characters to an ascii string or an ascii constant.
(ascii)"\u1234" // errorStrings a single character in length can also be exactly converted to a char or wchar constant:
char c; wchar u; c = "b"; // c is assigned the character 'b' u = 'b'; // u is assigned the wchar character 'b' u = 'bc'; // error - only one wchar character at a time u = "b"[0]; // u is assigned the wchar character 'b' u = \r; // u is assigned the carriage return wchar character
str.append(0); printf("the string is '%s'\n", (char *)str);The second way is to use the precision specifier. The way D arrays are laid out, the length comes first, so the following works:
printf("the string is '%.*s'\n", str);In the future, it may be necessary to just add a new format specifier to printf() instead of relying on an implementation dependent detail.
int[char[]] b; // associative array indexed by character string b.length; // number of elements in the array b["hello"] = 3; // set value associated with "hello" to 3 func(b["hello"]); // pass 3 as parameter to func()Particular entries in an associative array can be removed with the delete operator:
delete b["hello"];The in-expression yields a boolean result indicating if a key is in an associative array or not:
if ("hello" in b) ...Associated arrays are supported for all following types.
Properties:
.length number of items in the array .keys return array of the keys
import stdio; // C printf() import file; // D file I/O int main (char[][] args) { int word_total; int line_total; int char_total; int[char[]] dictionary; printf(" lines words bytes file\n"); for (int i = 1; i < args.length; ++i) // program arguments { char[] input; // input buffer int w_cnt, l_cnt, c_cnt; // word, line, char counts int inword; int wstart; input = File.read(args[i]); // read file into input[] for (int j = 0; j < input.length; j++) { char c; c = input[j]; if (c == "\n") ++l_cnt; if (c >= "0" && c <= "9") { } else if (c >= "a" && c <= "z" || c >= "A" && c <= "Z") { if (!inword) { wstart = j; inword = 1; ++w_cnt; } } else if (inword) { char[] word = input[wstart .. j]; dictionary[word]++; // increment count for word inword = 0; } ++c_cnt; } if (inword) { char[] word = input[wstart .. input.length]; dictionary[word]++; } printf("%8ld%8ld%8ld %.*s\n", l_cnt, w_cnt, c_cnt, args[i]); line_total += l_cnt; word_total += w_cnt; char_total += c_cnt; } if (args.length > 2) { printf("-------------------------------------\n%8ld%8ld%8ld total", line_total, word_total, char_total); } printf("-------------------------------------\n"); char[][] keys = dictionary.keys; // find all words in dictionary[] for (int i = 0; i < keys.length; i++) { char[] word; word = keys[i]; printf("%3d %.*s\n", dictionary[word], word); } return 0; }