Intelligent code completion

Similar to other autocompletion systems, intelligent code completion is a convenient way to access descriptions of functions, particularly their parameter lists. It speeds up software development by reducing the amount of name memorization needed and keyboard input required. It also allows for less reference to external documentation as interactive documentation on many symbols (i.e. variables and functions) in the active scope appears dynamically in the form of tooltips while programming.[6]

Intelligent code completion works using an automatically generated in-memory database of classes, variable names, and other constructs that the application being edited defines or references. The "classic" implementation of IntelliSense works by detecting marker characters such as periods, or other separator characters, depending on the language. When the user types one of these characters immediately after the name of an entity having one or more accessible members (such as contained variables or functions), IntelliSense suggests matches in a pop-up window. The user can either accept the suggestion by typing a statement completion character (Tab ↹ or ↵ Enter)—or a language-specific marker (such as the semicolon for C++), or continue typing the name. Over time, IntelliSense determines which variable or function the user most likely wants.

The feature also lets the user select from a number of overloaded functions in languages that support object oriented programming. IntelliSense also displays a short description of a function in the pop-up window—depending on the amount of documentation in the function's source code.

Some code editing software provide intelligent code completion through a Language Server Protocol (LSP) server.

Research extends back to 1957, including spelling checkers for bitmap images of cursive writing and special applications to find records in databases in spite of incorrect entries. In 1961, Les Earnest, who headed the research on this budding technology, saw it necessary to include the first spell checker that accessed a list of 10,000 acceptable words.[7] Ralph Gorin, a graduate student under Earnest at the time, created the first true spelling checker program written as an applications program (rather than research) for general English text: Spell for the DEC PDP-10 at Stanford University's Artificial Intelligence Laboratory, in February 1971.[8] Gorin wrote SPELL in assembly language, for faster action; he made the first spelling corrector by searching the word list for plausible correct spellings that differ by a single letter or adjacent letter transpositions and presenting them to the user. Gorin made SPELL publicly accessible, as was done with most SAIL (Stanford Artificial Intelligence Laboratory) programs, and it soon spread around the world via the new ARPAnet, about ten years before personal computers came into general use.[9] Spell, its algorithms and data structures inspired the Unix ispell program.

Assume a C++ application being edited in Visual Studio has a class Foo with some member functions:

class Foo {
  public:
    void bar();
    void foo_bar(char c, int n);
};

When the developer references this class in source code, e.g.:

Foo foo;
foo.

as soon as the user types the period after foo, IntelliSense automatically lists all the available member functions (i.e. bar() and foo_bar()) and all the available member attributes (private and protected members can be identified by a padlock picture beside their names). The user can then select one by using the arrow keys and hitting a completion character when the correct member function is highlighted. When available, IntelliSense displays a short description of the member function as given in the source code documentation.

IntelliSense goes further by indicating the required parameters in another pop-up window as the user fills in the parameters. As the user types a variable name, the feature also makes suggestions to complete the variable as they are typed. IntelliSense continues to show parameters, highlighting the pertinent one, as the user types.

The user can "force" IntelliSense to show its pop-up list without context by using Ctrl+J or Ctrl+Space. In Visual Studio this displays the entire application domain object model available to the developer.

• Torre, Charles (24 January 2008). "Arjun Bijanki: Making Sense of VC Intellisense" (Video). Channel9. Microsoft.
• "Using IntelliSense". VS .NET 2003 (2015 ed.). MSDN. Archived from the original on 2005.
• "IntelliSpeed Tutorial" (Video). Visual Prolog.