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For function that manipulate strings, modern object-oriented languages, like C# and Java have immutable strings and return a copy (in newly allocated dynamic memory), while others, like C manipulate the original string unless the programmer copies data to a new string. See for example Concatenation below.
COBOL uses the STRING statement to concatenate string variables. MATLAB and Octave use the syntax "[x y]" to concatenate x and y. Visual Basic and Visual Basic .NET can also use the "+" sign but at the risk of ambiguity if a string representing a number and a number are together. Microsoft Excel allows both "&" and the function "=CONCATENATE(X,Y)".
Both the C# extension methods and the Java default methods allow a class to override the default implementation of the extension/default method, respectively. In both languages this override is achieved by defining a method on the class that should use an alternate implementation of the method.
In many programming languages, string concatenation is a binary infix operator, and in some it is written without an operator. This is implemented in different ways: Overloading the plus sign + Example from C#: "Hello, " + "World" has the value "Hello, World". Dedicated operator, such as . in PHP, & in Visual Basic [1] and || in SQL.
Most languages, such as C#, Java [15] and Perl, do not support implicit string literal concatenation, and instead require explicit concatenation, such as with the + operator (this is also possible in D and Python, but illegal in C/C++ – see below); in this case concatenation may happen at compile time, via constant folding, or may be deferred ...
In some programming languages an operator may be ad hoc polymorphic, that is, have definitions for more than one kind of data, (such as in Java where the + operator is used both for the addition of numbers and for the concatenation of strings). Such an operator is said to be overloaded.
In the fourth and fifth cases, list concatenation must be invoked. In the last case, string concatenation must be invoked. Thus, the name + actually refers to three or four completely different functions. This is an example of overloading or more specifically, operator overloading. Note the ambiguity in the string types used in the last case.
A string is a finite sequence of characters. The empty string is denoted by .The concatenation of two string and is denoted by , or shorter by .Concatenating with the empty string makes no difference: = =.