Version 6 (modified by Charles, 7 years ago)


Expression Tour

This is a "tour" of various kinds of expressions in Cobra. It is intended to help you learn Cobra by quickly highlighting some interesting expressions you can write. It is neither a reference nor an exhaustive list of features. It assumes that the reader has basic familiarity with programming.

Displaying Expression Values

One of the best ways is to display an expression's value is to use the Trace statement which will show the source code of the expression, its value and the location of the trace in the source code (filename, line number, etc.):

trace p.x, p.y
    trace: p.x=5; p.y=6; at Foo.cobra:6; in Foo.main

You can, of course, use a Print statement. On a related note, you can validate the value of an expression with an Assert statement.

print 'My name is', name
assert x > 0


Arithmetic has the usual infix operators and parentheses for grouping. Note that division with a single slash (/) gives a fractional value. Use a double slash (//) for "integer" division.

assert 4 / 5 = 0.8
assert 4 // 5 == 0
assert 6 / 5 == 1.2
assert 6 // 5 == 1

Augmented assignment operators can be used to change values:

i += 1
p.x *= 2

Underscores can be put in numbers to separate groups of digits for easier reading:

big = 10_000_000


to-do (& | << >> ~)


Boolean expressions include the literals true and false as well as operations such as and, or, not, comparisons and other tests.

obj.isActive = true
if obj.isActive, .doSomething

to-do (all, any, don't say ==true or ==false)


to-do (literals, immutable, common methods, stringbuilder, msdn reference)

Calling Methods

to-do (don't need empty parens, calling on "this", calling base)

Instantiating Types

to-do (use parens, keyword args for properties, combining enums, works on System.Type and dynamic)

Comparing Values

to-do (<>, is & is not vs. == & <>, 0<= i < 10, overriding .equals (and .getHashCode) and .compareTo)


to-do (list, array, set, dict, explicit creation, indexing, .get, membership(in and not in for lists, arrays, sets, dict.keys, dict.values) )



Type Membership

to-do (inherits, implements, if-inherits, alternative is virtual method)


to-do (to, to?)

If Expression


For Expression



to-do (nil, to ?, to !, coalesce ? and ?=, ! and !=)

Method References

to-do (ref obj.method)

Expressions in Contracts

to-do (old expr, a implies b, breakout to a method)

See Also