Static code analysis can find hundreds of opportunities in VBA code.
Rubberduck builds its own internal representation of the code, and then proceeds to analyze it. Each individual inspection can easily be disabled, or configured to issue inspection results at different severity levels ranging from
Use the Inspection Results toolwindow to review Rubberduck’s findings, search, filter, regroup results by inspection, location, type, or severity. Each inspection result comes with a detailed description of what’s being flagged and why, so you can make an enlightened decision.
Unless configured otherwise, Rubberduck automatically runs inspections after the a parser/resolver cycle completes (regardless of whether the inspection results toolwindow is displayed or not).
For the best experience, it would be recommended to first try Rubberduck with an empty project, add a new module, and write, say, a loop that counts 1 to 10 and outputs to the debug pane - then to parse that and review the inspection results; carefully review the inspection settings, and consider disabling the inspections that irreconcilably clash with your preferences: use meaningful names alone can easily produce hundreds upon hundreds of results if you’re not that much into using vowels, or if you, say, prefix all your variable names; these inspections can be re-enabled anytime you’re ready!
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Warns about 'Function' and 'Property Get' procedures whose return value is not assigned.
Both 'Function' and 'Property Get' accessors should always return something. Omitting the return assignment is likely a bug.
Warns about assignments that appear to be assigning an object reference without the 'Set' keyword.
Omitting the 'Set' keyword will Let-coerce the right-hand side (RHS) of the assignment expression. If the RHS is an object variable, then the assignment is implicitly assigning to that object's default member, which may raise run-time error 91 at run-time.
Identifies places in which an object is used but a procedure is required and a default member exists on the object.
Providing an object where a procedure is required leads to an implicit call to the object's default member. This behavior is not obvious, and most likely unintended.
Warns about 'Declare' statements that are using the obsolete/unsupported 'CDecl' calling convention on Windows.
The CDecl calling convention is only implemented in VBA for Mac; if Rubberduck can see it (Rubberduck only runs on Windows), then the declaration is using an unsupported (no-op) calling convention on Windows.
Flags usages of members marked as obsolete with an @Obsolete("justification") Rubberduck annotation.
Marking members as obsolete can help refactoring a legacy code base. This inspection is a tool that makes it easy to locate obsolete member calls.
Flags declarations where a type hint is used in place of an 'As' clause.
Type hints were made obsolete when declaration syntax introduced the 'As' keyword. Prefer explicit type names over type hint symbols.
Flags 'While...Wend' loops as obsolete.
'While...Wend' loops were made obsolete when 'Do While...Loop' statements were introduced. 'While...Wend' loops cannot be exited early without a GoTo jump; 'Do...Loop' statements can be conditionally exited with 'Exit Do'.
Flags modules that specify Option Base 1.
Implicit array lower bound is 0 by default, and Option Base 1 makes it 1. While compelling in a 1-based environment like the Excel object model, having an implicit lower bound of 1 for implicitly-sized user arrays does not change the fact that arrays are always better off with explicit boundaries. Because 0 is always the lower array bound in many other programming languages, this option may trip a reader/maintainer with a different background.
Flags modules that omit Option Explicit.
This option makes variable declarations mandatory. Without it, a typo gets compiled as a new on-the-spot Variant/Empty variable with a new name. Omitting this option amounts to refusing the little help the VBE can provide with compile-time validation.
Flags parameters that are passed by reference (ByRef), but could be passed by value (ByVal).
Explicitly specifying a ByVal modifier on a parameter makes the intent explicit: this parameter is not meant to be assigned. In contrast, a parameter that is passed by reference (implicitly, or explicitly ByRef) makes it ambiguous from the calling code's standpoint, whether the procedure might re-assign these ByRef values and introduce a bug.
Warns about 'Sub' procedures that could be refactored into a 'Function'.
Idiomatic VB code uses 'Function' procedures to return a single value. If the procedure isn't side-effecting, consider writing is as a 'Function' rather than a 'Sub' the returns a result through a 'ByRef' parameter.
Locates procedures that are never invoked from user code.
Unused procedures are dead code that should probably be removed. Note, a procedure may be effectively "not used" in code, but attached to some Shape object in the host document: in such cases the inspection result should be ignored.