Uniform function call syntax (UFCS) or uniform call syntax (UCS) or sometimes universal function call syntax is a

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

feature in D, Nim, Koka, and Effekt 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-orie ...

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''. Objects can contain data (called fields, attributes or properties) and have actions they can perform (called procedures or methods and impl ...

), by using the receiver as the first parameter and the given arguments as the remaining parameters. The same technique is used in the

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scripting language under the name "OOP notation". UFCS is particularly useful when function calls are chained (behaving similar to

pipes 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-circu ...

, or the various dedicated

operators Operator may refer to: Mathematics * A symbol indicating a mathematical operation * Logical operator or logical connective in mathematical logic * Operator (mathematics), mapping that acts on elements of a space to produce elements of another ...

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 map ...

s for passing values through a series of expressions). 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-o ...

s in some other languages. Another benefit of the syntax is related to completion systems in IDEs, 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

D programming language

int first(int[] arr) int[] addone(int[] arr) void main()

Nim programming language

type Vector = tuple[x, 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)

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. In 2016 it was proposed a second time for addition to C++ by

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and Herb Sutter, 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 functions); 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 mo ...

between classes. This was again, in 2023, proposed by Herb Sutter claiming new information and insights, as well as an experimental implementation in the cppfront compiler.

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 is 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