Re: method call on result of method call

Eric Sosman <esosman@ieee-dot-org.invalid>
Tue, 15 Jun 2010 08:38:11 -0400
On 6/14/2010 7:52 PM, patrol wrote:

 From Wikipedia: Reference(Computer Science)

"A reference is distinct from the data itself. Typically, a reference
is the physical address of where the data is stored in memory or in
the storage device. For this reason, a reference is often called a
pointer or address, and is said to point to the data."

This seems to be saying that a reference *is* synonymous with a
pointer. They both refer/point to the memory address where the data is
located. No?

     No. A reference is any kind of datum that allows you to
locate some other datum, the thing the reference refers to.
One particularly efficient type of reference, suitable for use
in a computer's memory, is an address. But that's by no means
the only possible kind of reference, nor the only kind used!

     - Imagine building a linked list where all the nodes inhabit
       a single array, and the links are array indices. (As it
       happens, the very first linked list I ever encountered was
       built this way.) The links are certainly references, yet
       they are not memory addresses.

     - Imagine managing a Map with smallish keys and very large
       values, too large to keep all of them in memory at once.
       You might very well "front" it with a Map<Key,DiskAddress>
       which tells you where to find the data in external storage.
       The "values" in this proxy Map are references.

     - "Ah, but a DiskAddress is just an address!" I hear you cry.
       Well, then, consider a Map<Key,DatabaseKey> instead, where
       the DatabaseKey value locates the desired data, but only
       after some amount of further work by the database.

     - ""
       is itself a reference: A datum that leads to another. Yet it
       is certainly not a memory address!

Eric Sosman

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