” Ad hoc” in English does not a synonym of “this” or “such”, so you’d be changing the meaning of the sentence if you used “such” and “ad hoc” interchangeably.

If you need a specific purpose, look at that definition you quoted: “Created or done for a particular purpose as necessary. If you wanted to rewrite this sentence and just skip Latin, try writing something like: “A tuple is always a custom-built structure,

and take out a tuple for a

particular purpose.” Then to take out that tuple you can use a sentence’s actual meaning as. ”

Interestingly,
for the designers whose software/app is paid without a job, custom-built is considered ad hoc. @eques: ” ” ” For the authors of Wikipedia, ” ad hoc” has a slightly different connotation than custom-built. As @eques comments below, ad hoc has a slightly different connotation. Should a product be built on-the-fly but have never been designed before? Sometimes ad hoc can even have a negative meaning (as something that’s slapped together quickly as a temporary solution, but is probably badly designed and should be replaced), but that isn’t the case in this particular example.

Here’s an example of ad hoc: We cut a hole in

the wall and put a fan in it as an ad hoc cooling system for the server room, but eventually management will have to replace the air conditioning unit with a more powerful one.

What are some examples?

The two sentences in this paragraph are grammatically similar, different from each other.

A tuple is always such a structure…

This means that the tuple is a structure with characteristics that we’ve been discussing or that we’re about to discuss. When the part is after a colon is the description that described “such a” is referring to.

It means that a tuple is designed in

the moment to solve an immediate problem. Should an idea have any possible benefits?

In this case the part after the colon provides some explanations of the disadvantages from using this ad hoc solution. What is the meaning of ad hoc?

I believe the distinction your text may be making about a tuple with ad hoc is that the tuple is either a “scratch” or ephemeral copy of a row from a persistent table, or a row instantiated as-needed without the underpinnings of a persistent table. Singularity on columns vs. rows is an example of a tightly coupled table object having two tuples and also involving the pair of cells in a table. Therefore, because there is no tightly coupled object to enforce sameness with respect to the number of columns or sameness of datatype for a table, comparing them one to the other can be tricky. Enforcement of sameness requires metadata stored in a table definition. A tumulus has no such “baggage” to explain itself.

Ad hoc is better understood as only applying to this in its English usage. If you create an ad hoc report you are creating a one-off report, a report that you only use when the particular circumstance in which you created it.

What is your sentence saying is that, since the number of members of a tuple is unknown as part of its definition, any structure conforming to it must evaluate the contents of the tree at the time of its creation. That means that it must be created for this tuple only.