Gambas

The basic purpose, scope and principles of the document remain unchanged. ,

Overview

Gambas is a programming language and IDE.

Overview

• intended to fill the same niche as VB, though not intended to be code-compatible
• currently only available for Linux and other Unix-derivatives (there is a partially-functioning Windows version)
• open-source

Articles

• Gambas reference

Reference

• Gambas homepage
  • Gambas wiki is apparently written in Gambas, but requires an account in order to edit, which in turn requires an email to the author.
    • Gambas wiki now has a page history; not sure how it stacks up as a general-purpose wiki
    • Gambas wiki's search function uses Google, rather than being an internal search feature
• Wikipedia
• Wikibooks
• tutorials (English, Spanish)
• Linux Basic forum: ostensibly for "the new breed of Basics coming out for the Linux operating system", but the focus seems to be mostly (or entirely) on Gambas

resources

• Gambas IRC channel

How To

• Responding to right-clicks: the standard Click event also responds to right-clicks
• Showing a pop-up menu: still looking into this...

Stumbling Blocks

Unanswered

• Q: How do you access files shared via Samba? (One way would be to make use of the smb kioslave; how is that done in Gambas?)
• Q: Is it possible to do continuous forms as in MS Access? It seems likely that it can be done with some coding...
• Q: Is there any equivalent to the line-continuation syntax (space + underscore) in VB?
• Q: Is there a general language syntax tutorial or reference anywhere?
• Q: What do you do when an attempt to get Mouse information (e.g. Mouse.Right, to find out if the right button is being clicked) inside a Click event causes the error message "No mouse event data"? (The message box does not display an error number.)

Solved

• The "Not an object" error can mean that you tried to refer to a property as if it were a function, i.e. followed it with empty parentheses.
• Syntax for calling parameterless functions is deceptive. You can sometimes get away without using the parentheses, but other times you will get the function itself (presumably a pointer of some kind) as the return value instead of executing the funtion. When in doubt, always use parentheses.
  • Where the function returns an object, function.method seems to be ok (as long as "method" is not also a function)
• One of the more confusing aspects of Gambas (for a Visual Basic user, anyway) is that Gambas's events do not pass parameters; instead, you have to know where to fetch them from:
  • Form resize: the size is easily available as a form property ("ME.")
  • Mouse clicks: use the Mouse object
  • Key presses: use the Key object
  • Controls in a group: use the LAST keyword
    • The most obvious solution would have been for the event to pass the control as a parameter; Gambas events don't seem to use parameters. Another intuitive solution would have been for the group itself to appear on the form's list of controls/methods, as an alias for the currently active/effective control. Finally, if the form had an ActiveControl property, I could pull the .Tag value from there, although I would expect to run into problems using this technique under some circumstances. Answer: The LAST keyword refers to the control which generated the current event.
• Another minor thing to remember is that calls to Gambas subroutines always put parentheses around the parameter list (VB subroutines do not, unless the subroutine is a function or property and the return value is being retrieved).
• Q: How do you open a file-browsing dialog that uses KDE's kioslave feature? (DirChooser in gb.form lets you choose a local folder only.)
  • A: Dialog.SelectDirectory in gb.qt.kde provides this.
• An "invalid assignment" error can be caused by an undeclared variable, e.g. "A = B" if A has not been declared.
• Properties cannot accept additional arguments (other than the value being processed or retrieved). Workaround: instead of property Value, have function GetValue and sub PutValue(iVal). Not elegant, but functionally equivalent. Another option may be to have the passed data be a hash, but that is probably only efficient in certain rare circumstances; otherwise it involves extra coding to put the data in the hash and get it back out again.
• This may be a compiler bug or at least an undocumented feature: a class with no member variables seems to be automatically classified as "static", and therefore cannot be used with the NEW operator. To get around the problem, declare a dummy member variable (e.g. "private strDummy as string").

Flaws

• (Major) Apparently there is no way to instantiate virtual classes within Gambas; a descendant class must be written using C++. This means that you cannot effectively use any component (or other class), such as ListView, which returns data using virtual classes, without writing C++ code. Update: there is an INHERITS keyword which makes it sound like you actually can write a child class in Gambas; see inheritance for ongoing documentation.
• (Major, may be a problem for debugging) No "view stack" window
• (Major but livable) Hovering over variables at runtime does not display their current value, as in VB, nor does there seem to be any other way of inspecting values at runtime other than inserting debug code to display values.
• (Major but livable) Help is not context-sensitive
• (Major but livable) There is no equivalent to the VB right-click "Go to definition" menu command
• (Annoying; bad for writing good code) Constants cannot be defined using other constants (e.g. A = "something" & B, where A and B are both constants)
• (Puzzling) The error "Not enough arguments (#4)":
  • can appear at the point where a call to a subroutine has a problem inside the called subroutine, rather than at the point highlighted. (Use "RETURN" within the called subroutine to isolate the problem line, as Gambas will not let you step inside a subroutine when this problem happens.)
  • can be a sign of a property being called as a function
• (Minor) SHIFT-TAB does not reliably unindent (seems to work better when multiple rows are highlighted)
• (Minor) Although the syntax for accessing field data is nominally similar to VB's syntax, a variant which works under VB does not work in Gambas:

works in VB with objData intID = !ID strName = !Name end with

required form in Gambas intID = objData!ID strName = objData!Name

• (Minor) Identifiers are not automatically capitalized to match their declaration, as in VB; fortunately, identifiers are not case-sensitive for compilation, so this doesn't make things ugly the way it does in C/C++. (The pop-up list of methods/properties/events sometimes won't show up, however, unless the object's name is properly capitalized.)
• The field-list popup isn't smart in certain circumstances:
  1. Type me.controlname.field (use a real control name and a real field name)
  2. Move cursor somewhere else
  3. go back to same line, and highlight the "." between "controlname" and "field"
  4. type "."
     • (minor) The list doesn't automatically select the field which was there already
     • (annoying) When you select the field you want, it is inserted between "." and the fieldname that was there before. This follows logically from the editing rules, but is not what we want to happen; the selected fieldname should replace the old fieldname.

Notes

• The Help system appears to be wiki-based, possibly feeding directly off the Gambas wiki -- so any errors found can be corrected by anyone, in theory. Not sure how easy this is in practice. (Edit buttons do not appear in the Help app, so you would have to find the correct page on the wiki, and get editing permission from the webmaster.)