Why is the type of variable changing?

[garydown]

Trying to come to grips with AB field types. Why does the type change as below?

Buy = close;
_TRACE(typeof(buy));
Buy = IIf(False == False, False, False);
_TRACE(typeof(buy));

Buy = close;
_TRACE(typeof(buy));
Buy = false;
_TRACE(typeof(buy));

gives

[TrendSurfer]

@garydown,

See Understanding AFL.
See how-to-ask-a-good-question.

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[garydown]

Thanks TrendSurfer,
I am aware of verified badge requirement and am in the process of getting a license (awaiting reply to an email). As this is the presale/trial forum I would expect that simple questions like mine which may decide any future path would be acceptable.
I have read (several times) the suggested links.

Will try to improve my asking, but in the meantime I thought this would be such a simple thing (obviously not too simple as I had to ask).

Cheers.

[Tomasz]

AFL is dynamically typed. Which means that type of variable can change. The variable type depends on last assignment, so each assignment may change the type if you are assigning value that has different type.

REQUIRED reading:

Understanding how AFL works

In short Close is an array. False is constant equal to 0 (a number).

Note that numbers are accepted in places where functions expect arrays because of type coercion:

When scalar becomes an array, aka. type coercion in AFL

Since the subject of data types surfaced in this thread: Send orders to IB on next bar (Intraday) Here are some comments regarding data types in AFL. While some users who familiarized a bit with array handling in AFL may think that everything is an array in AFL, that is not the case. The data type depends on value assigned to variable. If you assign scalar (number) the variable type will be scalar (floating point number, 4 bytes long). So if you assign a number to variable like this: var1 =…

[garydown]

Thanks guys,
I re-read the articles and have achieved an array of zeros

buy = close - close;

As soon as I read the info again I remembered what I needed. Guess the sponge between my ears is a bit leaky.

[TrendSurfer]

@garydown

As this is the presale/trial forum I would expect that simple questions like mine which may decide any future path would be acceptable.

Yes - for your first 30 days.

@garydown

Guess the sponge between my ears is a bit leaky.

Everyone's sponge is leaky, key is to keep the sponge saturated (by learning) and then not let it go dry (keep learning / re-pouring).

[Tomasz]

@garydown - you do NOT NEED array of zeros. NEVER. In all places that require array
you can use just 0. Scalar (plain number) can be used in ALL places that accept array.
So no, you should not write close-close as it is waste of resources. Write 0 instead.

It is explained in link I already provided. JUST READ IT carefully. Don't skip When scalar becomes an array, aka. type coercion in AFL

[garydown]

Thanks Tomasz,
I am slowly coming to an understanding (have read through the doco few times now).
Amended the code to "=0" as suggested,
The next reference to the Buy variable does actually change it from a number to an array.

_TRACE("3 " + typeof(Buy));
                Buy[barI] = True;
_TRACE("4 " + typeof(Buy));

gives

It was this changing the type that was confusing me.

Thanks again,
Gary.

[Tomasz]

If you use subscript operator [index] on scalar (numeric) variable, it automatically gets upsized to array. This was explained in: When scalar becomes an array, aka. type coercion in AFL