= 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 [wiki: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.):

{{{
#!python
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 [wiki:Print] statement. On a related note, you can validate the value of an expression with an [wiki:Assert] statement.
{{{
#!python
print 'My name is', name
assert x > 0
}}}

== Arithmetic ==

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.
{{{
#!python
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:
{{{
#!python
i += 1
p.x *= 2
}}}

Underscores can be put in numbers to separate groups of digits for easier reading:
{{{
#!python
big = 10_000_000
}}}

== Bitwise ==

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

== Boolean ==

Boolean expressions include the literals `true` and `false` as well as operations such as `and`, `or`, `not`, comparisons and other tests.
{{{
#!python
obj.isActive = true
if obj.isActive, .doSomething
}}}

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

== Strings ==

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)

== Collections ==

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

== Slicing ==

to-do

== Type Membership ==

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

== Casting ==

to-do (to, to?)

== If Expression ==

to-do

== For Expression ==

to-do

== Nil ==

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 ==

 * LanguageTopics
 * HowToPrograms
 * LibraryTopics