4. Operators

To make it easier to write Pike, and to make the code somewhat shorter, some functions can be called with just one or two characters in the code. These functions are called operators and we have already seen how they work in plenty of examples. In this chapter I will describe in detail what they do. The operators are divided into categories depending on their function, but beware that some operators have meanings that go way beyond the scope of the category they are in.

The arithmetic operators are the simplest ones, since they work just like you remember from math in school. The arithmetic operators are:

The third column, "Identifier" is the name of the function that actually evaluates the operation. For instance, a + b can also be written as `+(a, b). I will show you how useful this can be at the end of this chapter.

When applied to integers or floats these operators do exactly what they are supposed to do. The only operator in the list not known from basic math is the modulo operator. The modulo operator returns the remainder from an integer division. It is the same as calculating a - floor(a / b) * b. floor rounds the value down to closest lower integer value. Note that the call to floor isn't needed when operating on integers, since dividing two integers will return the result as an integer and it is always rounded down. For instance, 8 / 3 would return 2.

If all arguments to the operator are integers, the result will also be an integer. If one is a float and the other is an integer, the result will be a float. If both arguments are float, the result will of course be a float.

However, there are more types in Pike than integers and floats. Here is the complete list of combinations of types you can use with these operators:

int + int

float + int
int + float
float + float

string + string
int + string
float + string
string + int
string + float

array + array

mapping + mapping

multiset + multiset

int - int

float - int
int - float
float - float

string - string

array - array

mapping - mapping

multiset - multiset

- int

- float

int * int

float * int
int * float
float * float

array(string) * string

array(array) * array

string * int

string * float

array * int

array * float

int / int

float / int
int / float
float / float

string / string

string / int

string / float

array / int

array / float

int % int

float % float
int % float
float % int

string % int

array % int

The arithmetic operators would be hard to use for anything interesting without the ability to compare the results to each other. For this purpose there are six comparison operators:

The == and != operators can be used on any type. For two values to be same they must be the same type. Therefore 1 and 1.0 are not same. Also, for two values of pointer types to be the same the two values must be pointers to the same object. It is not enough that the two objects are of the same size and contain the same data.

The other operators in the table above can only be used with integers, floats and strings. If you compare an integer with a float, the int will be promoted to a float before the comparison. When comparing strings, lexical order is used and the values of the environment variables LC_CTYPE and LC_LANG are respected.

Logical operators are operators that operate with truth values. In Pike any value except zero is considered true. Logical operators are a very basic part of Pike. They can also decide which arguments to evaluate and which not to evaluate. Because of this the logical operators do not have any identifiers and can not be called as normal functions. There are four logical operators:

These operators are used to manipulate bits as members in sets. They can also manipulate arrays, multisets and mappings as sets.

The first three operators can only be used with integers and should be pretty obvious.

The other three, intersection, union and symmetric difference, can be used with integers, arrays, multisets and mappings. When used with integers, these operators considers each bit in the integer a separate element. If you do not know about how bits in integers work I suggest you go look it up in some other programming book or just don't use these operators on integers.

When intersection, union or symmetric difference is used on an array each element in the array is considered by itself. So intersecting two arrays will result in an array with all elements that are present in both arrays. Example: ({7,6,4,3,2,1}) & ({1, 23, 5, 4, 7}) will return ({7,4,1}). The order of the elements in the returned array will always be taken from the left array. Elements in multisets are treated the same as elements in arrays. When doing a set operation on a mapping however, only the indices are considered. The values are just copied with the indices. If a particular index is present in both the right and left argument to a set operator, the one from the right side will be used. Example: ([1:2]) | ([1:3]) will return ([1:3]).

The index and range operators are used to retrieve information from a complex data type.

The index operator can be written in two different ways. It can be written as ob [ index ] or ob->identifier. However, the latter syntax is equal to ob [ "identifier" ].

You can only index strings, arrays, mapping, multisets and objects, and some of these can only be indexed on certain things as shown in this list:

string[int]

array[int]

array[int]=mixed

mapping[mixed]
mapping->identifier

mapping[mixed]=mixed
mapping->identifier=mixed

multiset[mixed]
multiset->identifier

multiset[mixed]=mixed
multiset->identifier=mixed

object[string]
object->identifier

object[string]=mixed
object->identifier=mixed

program[string]
program->identifier

string[int..int]

array[int..int]

When indexing an array or string it is sometimes convenient to access index from the end instead of from the beginning. This function can be performed by using a negative index. Thus  arr[-i]  is the same as arr[sizeof(arr)-i]. Note however that this behavior does not apply to the range operator. Instead the range operator clamps it's arguments to a suitable range. This means that a[b..c] will be treated as follows:

• If b is less than zero, the range will begin at the start of the array as if b had been zero.
• If b is greater or equal to sizeof(a) an empty array/string will be returned.
• If c is less than b, an empty array/string will be returned.
• If c is greater or equal to sizeof(a) the range will continue to the end of the array/string.
• No errors are generated in any of the above cases.

There is really only one assignment operator, but it can be combined with lots of other operators to make the code shorter. An assignment looks like this:

	variable = expression;

	variable1 = variable2 = 1; // Assign 1 to both variables
	variable1 =(variable2 = 1); // Same as above

	// Write the value of the expression, if any
	if(variable = expression)
	  write(variable);

In all of the above expressions variable can actually be any of type of assignable values. Assignable values are also known as lvalues and here is a list of lvalues:

Now there are only a couple of operators left. I have grouped them together in this section, not because they are not important, but because they do not fit in any particular categories.

The most important of these operators is the calling operator. It is used to call functions. The operator itself is just a set of parenthesis placed after the expression that returns the function. Any arguments to the function should be placed between the parenthesis, separated by commas. We have already seen many examples of this operator, although you might not have realized it was an operator at the time. The function call operator can do more than just calling functions though; if the 'function' is in fact an array, the operator will loop over the array and call each element in the array and returns an array with the results.

If on the other hand, the 'function' is a program, the operator will clone an object from the program and call create() in the new object with the arguments given. In fact, the function clone is implemented like this:

object clone(mixed p, mixed ... args) { ( (program)p )(@args); }

Then there are the increment and decrement operators. The increment and decrement operators are somewhat limited: they can only be used on integers. They provide a short and fast way to add or subtract one to an integer. If the operator is written before the variable (++a) the returned value will be what the variable is after the operator has added/subtracted one to it. If the operator is after the variable (a++) it will instead return the value of the variable before it was incremented/decremented.

Casting is used to convert one type to another, not all casts are possible. Here is a list of all casts that actually _do_ anything:

You can also use the cast operator to tell the compiler things. If a is a variable of type mixed containing an int, then the expression (int)a can be used instead of a and that will tell the compiler that the type of that expression is int.

Last, and in some respect least, is the comma operator. It doesn't do much. In fact, it simply evaluates the two arguments and then returns the right hand one. This operator is mostly useful to produce smaller code, or to make defines that can be used in expressions.

When evaluating an expression, you can always use parenthesis to tell the compiler in which order to evaluate things. Normally, the compiler will evaluate things from left to right, but it will evaluate operators with higher priority before those with lower. The following table shows the relative priority of all the operators in descending order:

Examples:

As mentioned earlier a + b can just as well be written as `+(a, b). Together with the function map which calls a function for every index in an array and the splice operator this can be used to create some very very fast and compact code. Let's look at some examples:

map(arr, `-)

This will return an array with each element negated.

map(text/"\n",`/," ")

This will divide a text into lines, each line will then be mapped through `/ and divided into an array of words.

`+(0, @arr)

This will add all the integers in the array arr together.

int abs(int a) { return ( a>0 ? `+ : `-)(a); }

This is a rather absurd but working function which will return the absolute value of a.