智能代碼補全

智能代碼補全是一種編程環境中，有上下文感知的的代碼自動完成功能。它可以通過減少打字錯誤和其他常見錯誤，使編寫應用的速度得到提升。智能代碼補全通常在鍵入、查詢函數參數以及與語法錯誤相關的查詢提示時，會彈出自動完成窗口。智能代碼補全和相關工具使用反射式編程產生變量名稱、函數和方法的文檔以及消除歧義。

該功能出現在許多編程環境中。其實現包括Atom中的 「autocomplete +」和Visual Studio Code中的 IntelliSense。該術語最初被命名為「選擇列表」，一些實現仍然這樣稱呼它。

## 概述

與其他自動完成系統相似，智能代碼補全可以便捷地訪問函數的定義，尤其是參數列表。這項功能因為減少鍵盤輸入和不需要記憶名稱，加速了軟體開發。它同時允許用戶更少地查閱外部文檔，由於許多在當前範圍的符號的交互式文檔會以提示框的形式動態顯現。

智能代碼補全使用記憶體里的自動生成資料庫，其中有類，變量名，和代碼中定義或提及的其他概念。典型的智能感知功能的實現，靠的是檢測「標記符」，例如句號（或者其他分隔符，由語言決定）。當使用者輸入有可訪問成員（比如成員變量或函數）的實體，緊接輸入此類字符時，立刻就彈出一個智能感知建議的彈窗。使用者可以通過鍵入一個完成語句的符號（Tab,Enter，或者在C++中的分號）接受建議，也可以繼續輸入。久而久之，智能感知會決定使用者最可能需要的變量或函數。智能感知還會憑藉函數的原始碼中的文檔，在彈窗內顯示函數的簡介。

在支持面向對象編程的語言中，這項功能也讓使用者從一系列重載的函數中選擇。一些代碼編輯軟體以語言伺服器的方式提供智能代碼補全功能。

## History

Research on intelligent code completion began in 1957, with spelling checkers for bitmap images of cursive writing and special applications to find records in databases despite 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. Ralph Gorin, a graduate student under Earnest at the time, created the first true spell-check program written as an application (rather than research) for general English text. SPELL, for the DEC PDP-10 at Stanford University's Artificial Intelligence Laboratory (SAIL), was published in February 1971. Gorin wrote the program in assembly for faster action; he made it by searching a 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 programs, and it soon spread around the world via the then-new ARPANET, about a decade before personal computers came into general use. SPELL and its algorithms and data structures inspired the Unix program Ispell.

## Support in editors and IDEs

### Visual Studio

IntelliSense is Microsoft's implementation of code completion, best known in Visual Studio. It was first introduced as a feature of a mainstream Microsoft product in 1996 building on many already invented concepts of code completion and syntax checking, with the Visual Basic 5.0 Control Creation Edition, which was essentially a publicly available prototype for Visual Basic 5.0. Initially, Visual Basic IDE was the primary "test bed" for the technology, but IntelliSense was incorporated into Visual FoxPro and Visual C++ in the Visual Studio 97 timeframe (one revision after first seen in Visual Basic). Because it was based on the introspection capabilities of COM, the Visual Basic versions of IntelliSense were always more robust and complete than the 5.0 and 6.0 (97 and 98 in the Visual Studio naming sequence) versions of Visual C++, which did not have the benefit of being entirely based on COM. These shortcomings (criticized by many VC++ developers since the 97 release) have been largely corrected in the .NET product lines. For example, one of the most requested capabilities missing from the pre-.NET products was support for templates, which is now fully implemented.

IntelliSense has entered a new phase of development with the unified Visual Studio.NET environment first released in 2001, augmented by the more powerful introspection and code documentation capabilities provided by the .NET framework. IntelliSense is now supported by the Visual Studio editors for C++, C#, J#, Visual Basic, XML, HTML and XSLT among others. As of Visual Studio 2005, IntelliSense is now activated by default when the user begins to type, instead of requiring marker characters (though this behavior can be turned off). The IDE has the capability of inferring a greater amount of context based on what the developer is typing, to the point that basic language constructs such as and while are also included in the choice list. In 2017 Microsoft announced IntelliCode, which uses machine learning to infer exactly which language or library feature is likely to be intended at every keystroke. Initially available as an extension for C# only, it is expected to be built in to future releases of Visual Studio.

Visual Studio 2022 includes artificial-intelligence features that can automatically suggest entire lines of code based on surrounding context.

Other Microsoft products that incorporate IntelliSense include Expression Web, FrontPage 2003, Small Basic, the Visual Basic for Applications IDEs in the Microsoft Office products, Visual Studio Code and many others. SQL Server 2008 Management Studio has autocomplete for the SQL syntax.

### Eclipse

The Eclipse IDE has code completion tools that come packaged with the program. It includes notable support for Java, C++, and JavaScript code authoring.

The Code Recommenders Eclipse project used to provide powerful intelligent completion, but due to lack of resources, was dropped in Eclipse 2018–12, and then archived in July 2019.

### Vim

Vim Intellisense is an advanced code completion system for the Vim editor.

## Example

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

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

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

```cpp
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 or Ctrl. In Visual Studio this displays the entire application domain object model available to the developer.