Uniform Function Call Syntax (UFCS) or Uniform Calling Syntax (UCS) or sometimes Universal Function Call Syntax is a

programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming ...

feature in D and Nim that allows any

function Function or functionality may refer to: Computing * Function key, a type of key on computer keyboards * Function model, a structured representation of processes in a system * Function object or functor or functionoid, a concept of object-oriente ...

to be called using the syntax for method calls (as in

object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of pr ...

), by using the receiver as the first parameter, and the given arguments as the remaining parameters. UFCS is particularly useful when function calls are chained (behaving similar to

pipe Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circula ...

s, or the various dedicated operators available in

functional language In computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that m ...

s for passing values through a series of

expression Expression may refer to: Linguistics * Expression (linguistics), a word, phrase, or sentence * Fixed expression, a form of words with a specific meaning * Idiom, a type of fixed expression * Metaphorical expression, a particular word, phrase, o ...

s). It allows free-functions to fill a role similar to

extension method In object-oriented computer programming, an extension method is a method added to an object after the original object was compiled. The modified object is often a class, a prototype or a type. Extension methods are features of some object-orie ...

s in some other languages. Another benefit of the method call syntax is use with " dot-autocomplete" in

IDEs Ides or IDES may refer to: Calendar dates * Ides (calendar), a day in the Roman calendar that fell roughly in the middle of the month. In March, May, July, and October it was the 15th day of the month; in other months it was the 13th. **Ides of Mar ...

, which use type information to show a list of available functions, dependent on the context. When the programmer starts with an argument, the set of potentially applicable functions is greatly narrowed down, aiding

discoverability Discoverability is the degree to which something, especially a piece of content or information, can be found in a search of a file, database, or other information system. Discoverability is a concern in library and information science, many aspects ...

Examples

Nim programming language

type Vector = tuple , y: int proc add(a, b: Vector): Vector = (a.x + b.x, a.y + b.y) let v1 = (x: -1, y: 4) v2 = (x: 5, y: -2) # all the following are correct v3 = add(v1, v2) v4 = v1.add(v2) v5 = v1.add(v2).add(v4)

D programming language

import std.stdio; int first(int[] arr) int[] addone(int[] arr) void main()

C++ proposal

Proposals for a unification of member function and free function calling syntax have been discussed from the early years of C++ standardization. Glassborow (2004) proposed a Uniform Calling Syntax (UCS), allowing specially annotated free functions to be called with member function notation. It has more recently been proposed (as of 2016) for addition to C++ by

Bjarne Stroustrup Bjarne Stroustrup (; ; born 30 December 1950) is a Danish computer scientist, most notable for the invention and development of the C++ programming language. As of July 2022, Stroustrup is a professor of Computer Science at Columbia University. ...

and

Herb Sutter Herb Sutter is a prominent C++ expert. He is also a book author and was a columnist for Dr. Dobb's Journal. He joined Microsoft in 2002 as a platform evangelist for Visual C++ .NET, rising to lead software architect for C++/CLI. Sutter has ser ...

, to reduce the ambiguous decision between writing free functions and member functions, to simplify the writing of templated code. Many programmers are tempted to write member functions to get the benefits of the member function syntax (e.g. " dot-autocomplete" to list

member function A method in object-oriented programming (OOP) is a procedure associated with a message and an object. An object consists of ''state data'' and ''behavior''; these compose an ''interface'', which specifies how the object may be utilized by any of ...

s); however, this leads to excessive

coupling A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end mov ...

between classes.

Rust usage of the term

Until 2018 it was common to use this term when actually referring to
qualified/explicit path syntax
' and most commonly the

'': because it's possible to have several traits defining the same method implemented on the same struct, a mechanism is needed to disambiguate which trait should be used. Member functions can also be used as free functions through a qualified (namespaced) path. The term UFCS is incorrect for these uses, as it allows using methods as (namespaced) free functions, but not using free functions as methods.

References