View source for Arrow operator

[[category:Operators]]
== <code>x->member</code> ==

The arrow operator accesses a member or invokes a member function of an atomic value. This can be distinguished from the ''[[Dot operator::A.I|dot operator, A.I]]'' which operates on <code>A</code> at the ''array level''. For example, suppose <code>x</code> is an array, then
:<code>x->member</code>
would [[Array Abstraction|array abstract]], applying the operator separately to every cell value of <code>x</code>. Whenever <code>x</code> is [[Null]], the result value is [[Null]].

The arrow can be typed either as a sequence of two characters, <code>-&gt;</code>, or as the single right-arrow character, <code>&rarr;</code>. [[Entering extended characters|To type the right-arrow character]] in Analytica, type the sequence: 
:<code>\rarr</code>[TAB]
where [TAB] is the tab key.

This operator only makes sense on certain atomic data types. Data types that include member fields (so that the variant <code>x&rarr;member</code> is meaningful) include:
* [[COM_Integration#The_Invoke_Method_operator|COM objects]]  
* [[Using_Python_from_Analytica#Arrow_operator_.28-.3E.29|Python classes]]

=== Member assignment ===
In some contexts, with some data types, you can assign to a member using the syntax
:<code>x->member := newValue;</code>
The right-hand side here is an expression that is evaluated.

==  <code>x &rarr; memberFn(...)</code> ==
Some data types include named member functions that can be called using the syntax
:<code>x -> memberFn( a, b, c )</code>
Unlike standard function calls, the Analytica parser cannot detect whether the member function exists or has a compatible set of parameters. These determinations occur at evaluation time. 

Some data types that have named member functions include:
* [[COM_Integration#The_Invoke_Method_operator|COM objects]]  
* [[Using_Python_from_Analytica#Arrow_operator_.28-.3E.29|Python classes]]

== <code> x &rarr; (...) </code> ==
Some data types are ''callables'' themselves (rather than having a named member function that is callable). These are called using the syntax
:<code>x -> (a,b,c)</code>

Data types that are directly callable include:
* [[Local functions]]
* [[Using_Python_from_Analytica#Arrow_operator_.28-.3E.29|Python classes]] (the class constructor)

== <code>x &rarr; [i] </code> ==
''New to [[Analytica 6.6]]''

Some data types have indexable content in which internal elements can be accessed using the syntax, e.g.,
:<code>x->[5]</code>
Data types in this category include:
* Text values, e.g., <code>"Hello world"->[5]</code> returns <code>"o"</code>. 
*:This is the same as <code>[[SelectText]]("Hello world", 5,  5)</code>
* [[In-memory binary data terms|Binary data terms]], in which x->[5] returns the fifth byte as an integer between 0 and 255.

=== <code>x &rarr; [m..n] </code> ===
The dot-dot operator can be placed inside the brackets to indicate that you want a subsequence rather than a single element. In addition, either «m» or «n» can be omitted to indicate "from the beginning" or "to the end". For example:
* <code>"Hello world"->[5..8]</code> returns <code>"o wo"</code>
* <code>"Hello world"->[.. 8]</code> returns <code>"Hello wo"</code>
* <code>"Hello world"->[5..]</code> returns <code>"o world"</code>

When <code>x</code> is a [[[[In-memory binary data terms|Binary data term]] and a dot-dot is used in the brackets, the result is a new, smaller, binary data term.

The use of dot-dot inside the brackets is a special case as is ''not''  the same as these:
* <code>[[Local]] s:=5..8 Do x->[s]</code>
* <code>x->[ [[Sequence]](5,8) ]</code>
These examples  would return lists of elements rather than sub-sequences of the original.

== See also ==
* [[COM Integration]]
* [[Using Python from Analytica]]
* [[Dot operator::A.I|dot operator, A.I]]
* [[In-memory binary data terms]]