Nomes de elementos declarados (Visual Basic)

Artigo
08/08/2011

Every declared element has a name, also called an identifier, which is what the code uses to refer to it.

Rules

An element name in Visual Basic must observe the following rules:

It must begin with an alphabetic character or an underscore (_).
It must only contain alphabetic characters, decimal digits, and underscores.
It must contain at least one alphabetic character or decimal digit if it begins with an underscore.
It must not be more than 1023 characters long.

The length limit of 1023 characters also applies to the entire string of a fully qualified name, such as outerNamespace.middleNamespace.innerNamespace.thisClass.thisElement.

The following example shows some valid element names.

aB123__45

_567

The following example shows some invalid element names. The first contains only an underscore, the second begins with a decimal digit, and the third contains an invalid character ($).

' Three INVALID element names

12ABC

xyz$wv

Aviso

Element names starting with an underscore (_) are not part of the CLS (Common Language Specification) (CLS), so CLS-compliant code cannot use a component that defines such names. However, an underscore in any other position in an element name is CLS-compliant.

Name Length Guidelines

As a practical matter, your name should be as short as possible while still clearly identifying the nature of the element. This improves the readability of your code and reduces line length and source-file size.

On the other hand, your name should not be so short that it does not adequately describe what the element represents and how your code uses it. This is important for the readability of your code. If somebody else is trying to understand it, or if you yourself are looking at it a long time after you wrote it, suitable element names can save a considerable amount of time.

Escaped Names

Generally, an element name must not match any of the keywords reserved by Visual Basic, such as Case or Friend. However, you can define an escaped name, which is enclosed by brackets ([ ]). An escaped name can match any Visual Basic keyword, since the brackets remove any ambiguity. You also use the brackets when you refer to the name later in your code.

In general, you should use escaped names only when:

Your code has migrated from a previous version of Visual Basic that did not reserve the keyword being used as a name; or
You are working with code written in another language in which the given keyword is not reserved.

Otherwise, you should consider renaming the element if its name conflicts with a keyword. The integrated development environment (IDE) provides an easy way to do this. For more information, see Como: Renomear um identificador (Visual Basic).

Case Sensitivity in Names

Element names in Visual Basic are case-insensitive. This means that when the compiler compares two names that differ in alphabetic case only, it interprets them as the same name. For example, it considers ABC and abc to refer to the same declared element.

However, the common language runtime (CLR) uses case-sensitive binding. Therefore, when you produce an assembly or a DLL and make it available to other assemblies, your names are no longer case-insensitive. For example, if you define a class with an element called ABC, and other assemblies make use of your class through the common language runtime, they must refer to the element as ABC. If you subsequently recompile your class and change the element's name to abc, the other assemblies using your class could no longer access that element. Therefore, when you release an updated version of an assembly, you should not change the alphabetic case of any public elements.