Ticket #122: const.patch

Source/Members.cobra

@@ -379 +379 @@
     inherits BoxMember
     implements IVar
     """
-    A BoxVar is a variable declared for a box, whether instance or shared. For example:
+    A BoxVar is a variable or constant declared for a box, whether instance or shared. For example:
         var _x as int is shared
+        const PI = 3.14
 
     Classes and structs can have vars, but interfaces cannot.
     
@@ -392 +393 @@
     var _initExpr as Expr?
     var _ifInheritsStack as Stack<of IType>
     var _isAssignedTo as bool
+    var _isConst as bool
 
     def init(token as IToken, box as Box, name as String, typeNode as ITypeProxy?, isNames as List<of String>, initExpr as Expr?, attribs as AttributeList?, docString as String)
         base.init(token, box, name, isNames, attribs ? AttributeList(), docString)
@@ -411 +413 @@
         .addField('initExpr', _initExpr)
 
     get englishName as String is override
-        return 'variable member'
+        return if(_isConst, 'constant member',  'variable member')
 
     pro isAssignedTo from var
 
@@ -419 +421 @@
 
     get requiresDotPrefix as bool
         return not _name.startsWith('_')
+        
+    def makeConstant
+        _isConst = true 
+        
+    get isShared as bool
+        return _isConst or base.isShared
 
     def attemptAssignmentOf(type as IType) as bool
         # TODO: dup'ed with AbstractLocalVar
@@ -454 +462 @@
                 _type = _initExpr.type
             else if not _initExpr.canBeAssignedTo(_type to !)
                 .throwError('Incompatible types. Cannot assign value of type [_initExpr.type.name] on the right to [_type.name] on the left.')
+        if _isConst and not _initExpr
+            .throwError('Cobra const must be explicitly initialised on declaration')
+            # enforce all upcase on const names?    
 
     get resultType as IType is override
         """

Source/BackEndClr/SharpGenerator.cobra

@@ -1518 +1518 @@
         base.writeSharpDef(sw)
         .writeSharpAttribs(sw)
         .writeSharpIsNames(sw)
+        if _isConst, sw.write('const ')
         sw.write(_type.sharpRef)
         sw.write(' [_backEndName]')
         if _initExpr

Source/KeywordSpecs.cobra

@@ -87 +87 @@
                 'set         | declarative: Declare property writer/mutator.',
                 'pro         | declarative: Declare a property.',
                 'var         | declarative: Declare a variable at the object or type level. Also, used as `from var` in property declarations. | expression: Refer to the variable that matches the containing property name.',
+                'const       | declarative: Declare a constant at the object or type level.',
                 'from        | declarative: Specify the backing variable for a property. Also, may be used for future LINQ syntax.',
                 'has         | declarative: Specify attributes to attach to the containing declaration.',
                 'body        | declarative: Declare the body of a method, indexer or property after blocked contracts or unit tests.',

Source/CobraParser.cobra

@@ -991 +991 @@
                     on 'GET', .addDecl(box, .declareGetOnlyProperty)
                     on 'SET', .addDecl(box, .declareSetOnlyProperty)
                     on 'PRO', .addDecl(box, .declareProperty)
-                    on 'VAR', .addDecl(box, .boxVarDecl)
+                    on 'VAR', .addDecl(box, .boxVarDecl(true))
+                    on 'CONST', .addDecl(box, .boxVarDecl(false))
                     on 'INVARIANT', .declareInvariant
                     on 'EOL', .endOfLine
                     on 'ENUM', .addDecl(box, .enumDecl)
@@ -1032 +1033 @@
         .grab
         .endOfLine
 
-    def boxVarDecl as BoxVar
-        .expect('VAR')
+    def boxVarDecl(isVar as bool) as BoxVar
+        .expect(if(isVar, 'VAR', 'CONST'))
         tok = .expect('ID')
         identifier = tok.text
         other = .curBox.declForName(identifier)
@@ -1046 +1047 @@
             numUnderscores += 1
         if not s.length
             .throwError('A class variable must be made of more than underscores. Try "[identifier]x" or "[identifier]1".')
-        if not s[0].isLower
+        if isVar and not s[0].isLower
             sugg = String(c'_', numUnderscores) + s[0].toString.toLower + s[1:]
             sugg = ' Try "[sugg]".'
             .throwError('Class variables must start with lowercase letters (after the underscore(s)) to distinguish them from other types of identifiers.[sugg]')
@@ -1072 +1073 @@
             attribs = .hasAttribs
             docString = .docString
             .dedent
-        return BoxVar(tok, .curBox, identifier, type, isNames, initExpr, attribs, docString)
-
+        bv = BoxVar(tok, .curBox, identifier, type, isNames, initExpr, attribs, docString)
+        if not isVar
+            bv.makeConstant
+        return bv
+                
     def declareInvariant
         .expect('INVARIANT')
         if .optional('COLON')

Tests/820-errors/400-declarations/520-constant.cobra

@@ +1 @@
+# Test const - compile time constant
+class AConst
+    const _uyear as int # .error.  const must be explicitly initialised on declaration
+    
+    def main is shared
+        pass

Tests/820-errors/400-declarations/522-constant.cobra

@@ +1 @@
+# Test const - compile time constant
+class AConst
+    const year = 1959
+
+    def init
+        # error currently generated by C# compiler, 
+        # shld probaby be caught by cobra
+        .year = 1967 # .error.
+        
+    def main is shared
+        pass
+        

Tests/820-errors/400-declarations/521-constant.cobra

@@ +1 @@
+# Test const - compile time constant
+class AConst
+    const YEAR as int = 1959
+    
+    def main is shared
+        # error currently generated by C# compiler, 
+        # shld probaby be caught by cobra
+        AConst.YEAR = 1967 # .error.
+

Tests/120-classes/224-fields-constant.cobra

@@ +1 @@
+# Test const - compile time constant
+class AConst
+    const YEAR as int = 1959
+    const pcode = 'xyzzy'
+    const _lastYear = .YEAR -1
+    var _nyear 
+    
+
+    def init
+        assert AConst.YEAR == 1959
+        assert .YEAR == 1959
+        assert _lastYear == 1958
+        assert .pcode == 'xyzzy'
+        _nyear = AConst.YEAR +1
+        
+    def main is shared
+        x = AConst()
+        
+        assert AConst.YEAR == 1959
+        assert AConst._lastYear == 1958
+        assert x._nyear == 1960
+

Developer/IntermediateReleaseNotes.text

@@ -9 +9 @@
 
 * Improved error checking on `listen` and `ignore` statements.
 
+* Support constant declarations on class instance variables: ticket:122
+
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 Library
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