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Name of a particular property

General and Gameplay Programming Programming

Started by Bacterius June 22, 2013 10:01 AM

12 comments, last by TheChubu 10 years, 9 months ago

Bacterius

13,181

Author

June 22, 2013 10:01 AM

Hello,

in my library I'm working on, I have a few functions which take (among other parameters) a data buffer, with the property that calling such a function twice in succession, with two data buffers, is equivalent to calling it once with the ordered concatenation of both data buffers. In other words:


F("hello")
F(" ")
F("world")

Is strictly equivalent to:


F("hello world")

Is there a name for such a property? For instance a function such that F(F(x)) = F(x) is called idempotent. I'm asking because I'm tired of describing this property in such a long-winded manner in my documentation, and it would be nice if there was a word I could use to sum it all up efficiently.

Thanks!

“If I understand the standard right it is legal and safe to do this but the resulting value could be anything.”

Paradigm Shifter

5,832

June 22, 2013 10:12 AM

Linear?

f(x + y) = f(x) + f(y)

(although linearity also means f(a*x) = a * f(x)).

"Most people think, great God will come from the sky, take away everything, and make everybody feel high" - Bob Marley

JD557

163

June 22, 2013 10:34 AM

I'm not an expert on the topic, but this ressembles a lot the way IO is handled in haskell via monads. You might want to look into that.

Here's a really nice explanation and some more monad examples.

alvaro

21,604

June 22, 2013 10:43 AM

I don't know of a name, but I can make one up: "concatenation invariant". :)

JD557

163

June 22, 2013 11:11 AM

Linear?

f(x + y) = f(x) + f(y)

(although linearity also means f(a*x) = a * f(x)).

This seems ok to me

print("A"+"B")=print("A")+print("B")

print(5*"A")=print("A"+"A"+"A"+"A"+"A")+print("AAAAA")

Bacterius

13,181

Author

June 22, 2013 11:18 AM

Linear?

f(x + y) = f(x) + f(y)

(although linearity also means f(a*x) = a * f(x)).

That would be fine for a couple of them but many of them do not actually return an output of the same size as the input (or at all) so in those instances "linear" would be meaningless, unfortunately.

I don't know of a name, but I can make one up: "concatenation invariant".

I like it

“If I understand the standard right it is legal and safe to do this but the resulting value could be anything.”

blutzeit

1,650

June 22, 2013 11:23 AM

As you're dealing with data buffer, it seems that the function is some kind of stream writing operator.

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Khatharr

8,814

June 25, 2013 09:36 AM

I don't know of a name, but I can make one up: "concatenation invariant".

How about "inconcatviant"?

void hurrrrrrrr() {__asm sub [ebp+4],5;}

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frob

46,221

June 25, 2013 04:23 PM

I have a few functions which take (among other parameters) a data buffer, with the property that calling such a function twice in succession, with two data buffers, is equivalent to calling it once with the ordered concatenation of both data buffers.

I don't think that is a very good idea.

When it comes to building a language, make it apply in ALL cases. Something that applies in only SOME cases is usually a bug.

For example, your example

Print("Hello"); Print(" "); Print("World!);

might just happen to be functionally equivalent to Print("Hello World!");

But it is not universally true of all string functions. It is very different from:

PrintLine("Hello"); PrintLine(" "); PrintLine("World!");

The result should be three distinct entries. It would be functionally equivalent to Print("Hello\n \nWorld!\n");

Or consider:

ShowDialog("Hello"); ShowDialog(" "); ShowDialog("World!");

I expect three distinct dialog boxes, not one single dialog box with the strings concatenated.

It is one thing to allow adjacent string literals to be concatenated. It is quite another thing to not call adjacent functions because their parameters happen to be the same type.

alvaro

21,604

June 25, 2013 05:17 PM

I have a few functions which take (among other parameters) a data buffer, with the property that calling such a function twice in succession, with two data buffers, is equivalent to calling it once with the ordered concatenation of both data buffers.

I don't think that is a very good idea.

[...]

I don't understand your objection. Perhaps you misread something? He is not saying that this property is universal, only that he has several functions with that property and he wants to know of a short way to describe it. It sounds very reasonable to me...

Name of a particular property

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