Changes between Initial Version and Version 1 of MultiArgAssign

Timestamp:

11/04/08 07:09:45 (16 years ago)

Author:

hopscc

Comment:

--

MultiArgAssign

@@ +1 @@
+= Multi Variable or Multi Target Assignments =
+
+Cobra supports multi variable or multi target assignment
+{{{
+a,b,c = 10,20,30  # comma separated list of expressions
+
+# or
+a,b,c = [10,20,30] # list literal
+
+# or
+alist = [10,20,20]
+a,b,c = alist       # an arbitrary list variable
+
+assert a == 10
+assert b == 20
+assert c == 30
+}}}
+These are expected to give the same results as if the assignment 
+target and source lists were unrolled and each assignment done individually
+{{{
+a = 10
+b = 20
+c = 30
+
+a = alist[0]
+b = alist[1]
+c = alist[2]
+}}}
+
+The targets must be a comma separated list, the items of which are
+things that can be assigned a value - any of local variables, 
+class or instance variables, properties or indexers.
+
+The assignment sources can be a single expression that resolves to a list, array or 
+String (specifically any expression that supports an integer indexer)[[BR]]
+ '''or'''
+a comma separated stream of expressions.
+
+{{{
+# unusual but acceptable - dict keyed by int in range
+dict = {1:'aye', 2:'bee'}
+a,b = dict
+assert a == 'aye'
+assert b == 'bee'
+
+# assignment to an expression list
+a,s,c = 99+1, 'xxx'+'y', 2*2
+assert a == 100
+assert x == 'xxxy'
+assert c == 4
+
+}}}
+
+The size of the target and source lists are expected to match as if the
+assignments were done individually.
+
+The target source values are atomic in value for the duration of the assignments.
+
+== multi Targets in a 'for loop' ==
+ 
+Multiple targets can also be provided in a for loop covering an enumerable
+source.
+
+If the enumerable source is a Dictionary there may be only 2 targets and they
+get filled with the next key and keyValue from the dictionary for the loop
+block
+
+{{{
+dict = {'x':'aye', 'y':'bee'}
+for k,v in dict
+    print 'key=,k, 'value=', v
+    assert k in '[x', 'y']
+    assert v in ['aye', 'bee']
+}}}
+
+Otherwise the enumerable source is expected to generate a list of items of
+the same size as the list of targets for each step of the enumeration
+{{{
+for i,j in [1,2,3,4]    # error
+    pass
+
+for i,j in [ [1,2], [3,4]]
+    assert i in [1,3]
+    assert j in [2,4]    
+
+}}}
+
+If you want to get multiple values from an enumeration generating non list
+(single) values the current idiom is to use a 
+[wiki:EnumForExpr for expression]
+{{{
+i,j = for x in [1,2,3,4] get x
+
+alist = [1,2,3,4]
+i,j = for x in alist get x
+}}}