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John Haugabook
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* resolve readme validate * Apply suggestions from code review Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com> Co-authored-by: John Haugabook <johnhaugabook@gmail.com> * rhino3d-scripts: rm reference to deprecated VBScript --------- Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
113 lines
3.2 KiB
Markdown
113 lines
3.2 KiB
Markdown
# VBScript Quirks for RhinoScript
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Things that bite when writing `.rvb` / `.vbs` files and aren’t obvious to anyone whose mental model is C-family or Python.
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## Always Start With `Option Explicit`
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Without it, mistyping a variable name silently creates a new `Variant` set to `Empty`. Every `.rvb` file should begin:
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```vbscript
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Option Explicit
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```
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## No Block Scope
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All `Dim` declarations inside a `Sub`/`Function` are hoisted to the top. A `Dim` inside an `If` block is visible after the `If` ends. Loop counters survive the loop.
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## `Nothing` vs `Empty` vs `Null`
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| Sentinel | Test with | Meaning |
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|---|---|---|
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| `Empty` | `IsEmpty(x)` | `Dim`’d but never assigned |
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| `Null` | `IsNull(x)` | Explicit “no value” — what `Rhino.GetObject` returns on cancel |
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| `Nothing` | `x Is Nothing` | An **object** reference that points to nothing — only for `Set` variables |
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Wrong sentinel → silently false.
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## Parentheses Change Semantics
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```vbscript
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Foo a, b ' Call a Sub or Function (return value discarded)
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Call Foo(a, b) ' Call a Sub or Function (return value discarded)
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x = Foo(a, b) ' Call a Function and capture the return
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Foo(a, b) ' SYNTAX ERROR for multi-arg subs
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Foo(x) ' Calls Foo passing x BY VALUE, even if Foo declares ByRef
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Foo x ' Honors Foo's ByRef declaration
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```
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If a Sub modifies its argument and your change isn’t taking effect — you wrapped the argument in parentheses.
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## `ByRef` Is the Default
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Unlike most languages, VBScript passes arguments **by reference by default**. Functions can mutate their callers’ variables. Be explicit:
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```vbscript
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Sub Increment(ByRef n)
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n = n + 1
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End Sub
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```
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## Arrays Are 0-Based But Have `UBound`, Not `Length`
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```vbscript
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Dim arr(2) ' Three elements: arr(0), arr(1), arr(2)
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For i = 0 To UBound(arr)
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arr(i) = i * 10
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Next
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```
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`Dim arr(n)` creates `n+1` elements. `ReDim Preserve arr(newSize)` resizes (only the last dimension of a multi-dim array).
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## `Set` Is Required for Object Assignment
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```vbscript
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Set fso = CreateObject("Scripting.FileSystemObject") ' correct
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fso = CreateObject("Scripting.FileSystemObject") ' RUNTIME ERROR
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```
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Any time the right-hand side is an object (COM object, RegExp, Dictionary), you must use `Set`.
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## Error Handling Is Manual
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```vbscript
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On Error Resume Next
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Rhino.AddCircle Array(0,0,0), -1
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If Err.Number <> 0 Then
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Rhino.Print "Failed: " & Err.Description
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Err.Clear
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End If
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On Error GoTo 0 ' Restore normal error behavior
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```
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`On Error Resume Next` suppresses **all** errors until `On Error GoTo 0`. Forgetting to restore is a common bug.
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## Points Are 3-Element Arrays
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Rhino expects `Array(x, y, z)`. A 2-element array (`Array(x, y)`) raises a type-mismatch error.
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```vbscript
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Dim pt
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pt = Array(1.0, 2.0, 3.0)
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Rhino.AddPoint pt
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```
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## String Concatenation Uses `&`, Not `+`
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`+` on strings works only if **both** sides are strings. If one side is a number, `+` does numeric addition and throws a type-mismatch. Always use `&`:
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```vbscript
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Rhino.Print "Count: " & n
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```
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## `For Each` Needs a `Variant`
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```vbscript
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Dim item
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For Each item In someCollection
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' ...
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Next
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```
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The loop variable must be `Variant`. You cannot `Dim item As Long` (VBScript has no typed `Dim`).
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