vb6-guidelines

VB6 Guidelines

VB6 is not VB.NET. It is not C#. It is not VBA. The rules below reflect what the VB6 compiler (1998) requires and what the COM ecosystem expects.

1. Case-preservation is absolute in existing code

VB6 is case-insensitive at the compiler level. Diff tools (Git, GitHub, GitLab, Bitbucket, code review tools) are case-sensitive. Changing the case of an identifier in existing code pollutes pull requests with ghost changes, hides the real diff, and breaks git blame.

Absolute rule: when editing existing code, the case of every identifier stays exactly as it is. No exceptions.

This applies to:

• Variables and parameters (m_StrName stays m_StrName even if the current convention is m_strName)
• Properties and procedures (Public Sub ReadFile is not "normalized" to ReadFile if it is already ReadFile)
• Keywords (If/Then/End If — preserve as written; the IDE may have normalized different files differently)
• Type names (As String, As Long)
• Constants (vbCrLf vs vbCRLF)
• References to module and class names

When you may use the "correct" case:

• New code (new procedure, new module, new variable)
• When the user explicitly asks for normalization

When you may not, even when it looks obvious:

• "Taking advantage" of a bugfix commit to normalize
• "Since I'm already here" during a legitimate refactor of something else
• Cosmetic cleanup without explicit request

The cost of polluting the diff outweighs the value of uniformity. Always.

2. Option Explicit and type declarations are mandatory

VB6 allows implicit typing for VB3/4 backward compatibility. In new code, this is guaranteed technical debt.

• Always Option Explicit at the top of every module (.bas, .cls, .frm)
• Always declare type: Dim i As Long, never Dim i
• Prefer Long over Integer — VB6 Integer is 16 bits, overflows at 32,768
• Avoid Variant except when interacting with APIs that return Variant (e.g., ADO GetRows)
• Declare return type in every Function: Public Function X() As String, not Public Function X()