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Author:halw

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Date:2009-03-27T20:47:18.000000Z


git-svn-id: https://svn.eiffel.com/eiffel-org/trunk@211 abb3cda0-5349-4a8f-a601-0c33ac3a8c38
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halw
2009-03-27 20:47:18 +00:00
parent 5d5de7df3d
commit 051ba553db
6 changed files with 49 additions and 39 deletions
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documentation/current/method/eiffel-tutorial-et/et-dynamic-structure-execution-model.wiki
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@@ -277,7 +277,7 @@ meaning that, at the time of each call, the value of each formal will be set to
In the routine body, it is not permitted to change the value of a formal argument, although it is possible to change the value of an attached object through a procedure call such as <code>formal_1.some_procedure ( ... )</code> .
==Infix and prefix notation==
==Infix and prefix notations==
Basic types such as <code>INTEGER</code> are, as noted, full-status citizens of Eiffel's type system, and so are declared as classes (part of the Kernel Library). <code>INTEGER</code>, for example, is characterized by the features describing integer operations: plus, minus, times, division, less than, and so on.
@@ -288,22 +288,22 @@ With the dot notation seen so far, this would imply that simple arithmetic opera
instead of the usual
<code>
i + j
</code>
This would be awkward. Infix and prefix features solve the problem, reconciling the object-oriented view of computation with common notational practices of mathematics. The addition function is declared in class <code>INTEGER</code> as
This would be awkward. Infix and prefix notations solve the problem, reconciling the object-oriented view of computation with common notational practices of mathematics. The addition function is declared in class <code>INTEGER</code> as
<code>
infix "+" (other: INTEGER): INTEGER
plus alias "+" (other: INTEGER): INTEGER
do
...
end
</code>
Such a feature has all the properties and prerogatives of a normal "identifier" feature, except for the form of the calls, which is infix, as in <code>i + j</code> , rather than using dot notation. An infix feature must be a function, and take exactly one argument. Similarly, a function can be declared as <code>prefix "-" </code>, with no argument, permitting calls of the form <code>-3</code> rather than <code>(3).negated</code> .
Such a feature has all the properties and prerogatives of both normal "identifier-dot" notation and infix notation. This allowing invoking <code>plus</code> using either notation: <code>i.plus (j)</code> or <code>i + j</code> . A feature such as <code>plus</code> allowing infix notation must be a function, and take exactly one argument.
Prefix notation is allowed as well. A function can be declared as <code>opposite alias "-" </code>, with no argument, permitting calls of the form <code>-3</code> rather than <code>(3).opposite</code> .
Predefined library classes covering basic types such as <code>INTEGER</code>, <code>CHARACTER</code>, <code>BOOLEAN</code>, <code>REAL</code>, <code>DOUBLE</code> are known to the Eiffel compiler, so that a call of the form <code>j + i</code>, although conceptually equivalent to a routine call, can be processed just as efficiently as the corresponding arithmetic expression in an ordinary programming language. This brings the best of both worlds: conceptual simplicity, enabling Eiffel developers, when they want to, to think of integers and the like as objects; and efficiency as good as in lower-level approaches.
Infix and prefix features are available to any class, not just the basic types' predefined classes. For example a graphics class could use the name <code>infix "|-|"</code> for a function computing the distance between two points, to be used in expressions such as
Infix and prefix notations are available to any class, not just the basic types' predefined classes. For example a graphics class could use the name <code>distance alias "|-|"</code> for a function computing the distance between two points, to be used in expressions such as
<code>
point1 |-| point2
</code>
@@ -354,7 +354,7 @@ expanded class
feature -- Basic operations
infix "+" (other: INTEGER): INTEGER
plus alias "+" (other: INTEGER): INTEGER
do
...
end