explicit indices in array literals

rod/msgs.nim

@@ -94,6 +94,7 @@ type
     errXCannotBeInParamDecl, errPragmaOnlyInHeaderOfProc, errImplOfXNotAllowed, 
     errImplOfXexpected, errNoSymbolToBorrowFromFound, errDiscardValue, 
     errInvalidDiscard, errIllegalConvFromXtoY, errCannotBindXTwice, 
+    errInvalidOrderInArrayConstructor,
     errInvalidOrderInEnumX, errEnumXHasWholes, errExceptExpected, errInvalidTry, 
     errOptionExpected, errXisNoLabel, errNotAllCasesCovered, 
     errUnkownSubstitionVar, errComplexStmtRequiresInd, errXisNotCallable, 
@@ -214,6 +215,7 @@ const
     "value returned by statement has to be discarded", 
     "statement returns no value that can be discarded", 
     "conversion from $1 to $2 is invalid", "cannot bind parameter \'$1\' twice", 
+    "invalid order in array constructor",
     "invalid order in enum \'$1\'", "enum \'$1\' has wholes", 
     "\'except\' or \'finally\' expected", 
     "after catch all \'except\' or \'finally\' no section may follow", 

rod/semexprs.nim

@@ -260,11 +260,29 @@ proc semArrayConstr(c: PContext, n: PNode): PNode =
   if sonsLen(n) == 0: 
     addSon(result.typ, newTypeS(tyEmpty, c)) # needs an empty basetype!
   else: 
-    addSon(result, semExprWithType(c, n.sons[0]))
+    var x = n.sons[0]
+    var lastIndex: biggestInt = 0
+    var indexType = getSysType(tyInt)
+    if x.kind == nkExprColonExpr: 
+      var idx = semConstExpr(c, x.sons[0])
+      lastIndex = getOrdValue(idx)
+      indexType = idx.typ
+      x = x.sons[1]
+    
+    addSon(result, semExprWithType(c, x))
     var typ = skipTypes(result.sons[0].typ, {tyGenericInst, tyVar, tyOrdinal})
     for i in countup(1, sonsLen(n) - 1): 
-      n.sons[i] = semExprWithType(c, n.sons[i])
+      x = n.sons[i]
+      if x.kind == nkExprColonExpr:
+        var idx = semConstExpr(c, x.sons[0])
+        idx = fitNode(c, indexType, idx)
+        if lastIndex+1 != getOrdValue(idx):
+          liMessage(x.info, errInvalidOrderInArrayConstructor)
+        x = x.sons[1]
+      
+      n.sons[i] = semExprWithType(c, x)
       addSon(result, fitNode(c, typ, n.sons[i]))
+      inc(lastIndex)
     addSon(result.typ, typ)
   result.typ.sons[0] = makeRangeType(c, 0, sonsLen(result) - 1, n.info)
 

tests/accept/run/spec.csv

@@ -2,6 +2,7 @@ tack.nim;125
 tambsym2.nim;7
 tambsys.nim;
 tarray.nim;10012
+tarraycons.nim;6
 tarray2.nim;[16, 25, 36]
 tarray3.nim;3
 tassert.nim;assertion failure!this shall be always written

tests/accept/run/tarraycons.nim

@@ -0,0 +1,17 @@
+
+type
+  TEnum = enum
+    eA, eB, eC, eD, eE, eF
+    
+const
+  myMapping: array[TEnum, array[0..1, int]] = [
+    eA: [1, 2],
+    eB: [3, 4],
+    [5, 6],
+    eD: [0: 8, 1: 9],
+    eE: [0: 8, 9],
+    eF: [2, 1: 9]
+  ]
+
+echo myMapping[eC][1]
+

tests/reject/spec.csv

@@ -3,6 +3,7 @@ tadrdisc.nim;15;for a 'var' type a variable needs to be passed
 tambsym.nim;6;ambiguous identifier
 tambsym2.nim;4;undeclared identifier: 'CreateRGBSurface'
 tambsym3.nim;6;ambiguous identifier
+tarraycons.nim;9;invalid order in array constructor
 tatomic.nim;2;identifier expected, but found 'atomic'
 tbind2.nim;7;ambiguous call
 tbind4.nim;4;undeclared identifier: 'lastId'

tests/reject/tarraycons.nim

@@ -0,0 +1,17 @@
+
+type
+  TEnum = enum
+    eA, eB, eC, eD, eE, eF
+    
+const
+  myMapping: array[TEnum, array[0..1, int]] = [
+    eA: [1, 2],
+    eC: [3, 4],
+    eB: [5, 6],
+    eD: [0: 8, 1: 9],
+    eE: [0: 8, 9],
+    eF: [2, 1: 9]
+  ]
+
+echo myMapping[eC][1]
+

todo.txt

@@ -2,7 +2,6 @@
 - deprecate ^ and make it available as operator
 - test branch coverage
 - checked exceptions
-- explicit indices for array literals
 - built-in serialization
 - do not ambiguity error for methods if amibiguity only affects the same 
   dispatcher anyway

web/news.txt

@@ -47,6 +47,8 @@ Additions
 - A field in an ``enum`` may be given an explicit string representation. 
   This yields more maintainable code than using a constant 
   ``array[TMyEnum, string]`` mapping.
+- Indices in array literals may be explicitly given, enhancing readability:
+  ``[enumValueA: "a", enumValueB: "b"]``.