Still with software science translations.. Now I'm coming to you with this expression that have always bothered me: "on the fly"

How the hood would you translate that *elegantly* to spanish?

It feels like "sobre la marcha" is way overkill, at least from a structure point of view. Also "al toque", sounds maybe too coloquial.

What do you think?

edit: so the english sentence could be:

> 
> The value is returned from a new function executed on the fly.
> 
> 
>
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No, I don’t like very much `sobre la marcha`. I mean, not always, and in “*software science translations*” almost never. I don’t feel it translate the whole idea exactly, with sometimes is: immediately and automatically, without user’s or external elements intervention. 

There are many other possibilities. 

My favorite is the simple direct translation: “`al vuelo`”.

Let’s see what the RAE said about “vuelo”:

> 
> al ~, o a ~.
> 
> 
> 1. locs. advs. Con prontitud.
> 
> 
> cazarlas alguien al ~.
> 
> 
> 1. loc. verb. Entender o notar con prontitud las cosas que no se dicen claramente o que se hacen ocultamente.
> 
> 
> coger al ~ algo.
> 
> 
> 1. loc. verb. Lograrlo de paso o casualmente.
> 
> 
> cogerlas alguien al ~.
> 
> 
> 1. loc. verb. coloq. cazarlas al vuelo.
> 
> 
> alzar el ~.
> 
> 
> 1. loc. verb. Echar a volar.
> 2. loc. verb. coloq. Marcharse de repente.
> 
> 
> 

I like this more than “`sobre la marcha`”, with the bonus that many people will automatically translate it to `on the fly` with the exact original meaning.

Some of the other possibilities are:

“sobre la marcha” (of course),

inmediátamente,

automáticamente, 

dinámicamente (this is probably my second favorite). *The windows layout change on the fly.* **El diseno de la pantalla cambia dinámicamente.** (a sort of this)

simultáneamente 

Let’s see some concrete examples:

[I have a class which calculates it's property on-the-fly, for example:](https://stackoverflow.com/q/15744634/1458030)

Tengo una clase que calcula sus propiedades al vuelo. (dinámicamente, en tiempo real)(I’m not sure how to correctly translate `class` and `properties`)

[An example enlightens the kerning-on-the-fly functionality:](https://stackoverflow.com/q/12654826/1458030)

Un ejemplo aclara esta funcionalidad de posicionamiento al vuelo. (dinámico, instantaneo, sobre la marcha)

[Encryption on the fly.](https://stackoverflow.com/q/16215990/1458030) 
Cifrado al vuelo. Cifrado simultaneo, en tiempo real, dinámico, automático…

On the fly translation. 
Traduccion simultanuea. (al vuelo, instantanea, sobre la marcha)

[More examples are here.](http://www.linguee.com/english-spanish?query=on%20the%20fly&source=english)
I would generally use *sobre la marcha* and I don't see it as overkill.

What does this phrase have to do with Scientific translations? Maybe a few examples would help.