I think this tag could apply to several of the posts on this site, and is a good canonical name describing the intention of a challenge.

It could possibly be a tag accommodating different types of challenges, but I see it as mostly accommodating a challenge. A challenge would be given this tag if it asks to create a function or language construct to accomplish a task, and restricts answers from using the language's exact and similar built-ins within the implementation.

I find that fleshing out exactly what "similar" means in this case would be in the interest of the community to balance creativity and close loopholes in the spirit of preventing the challenge from becoming too trivial. My question, however, is not proposing to define what that means yet though, just whether this tag should exist or not.

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    \$\begingroup\$ Isn't that just restricted-source? \$\endgroup\$
    – Dennis
    Commented Jul 7, 2016 at 18:45
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    \$\begingroup\$ @Dennis No, restricted source imposes restrictions on the source code itself, e.g. no numbers. This is proposing a tag that denotes that the challenge is about performing a common task without built-ins. \$\endgroup\$
    – Alex A.
    Commented Jul 7, 2016 at 18:46
  • \$\begingroup\$ @Dennis it's a specific type of restricted-source. That tag only implies there is a restriction, but it does not necessarily mean that the restriction is related directly to the task being implemented. \$\endgroup\$ Commented Jul 7, 2016 at 18:46

2 Answers 2



I don't think such a tag is necessary, nor would it be a good idea. At what point is a task considered common? For example, is implementing a fast Fourier transform common? Perhaps for some it is, and for many it isn't. "Common" can't be precisely defined. As such there wouldn't be an objective way to determine whether the tag is appropriate for a given challenge.

  • \$\begingroup\$ What if I removed the qualifier "common"? e.g. implement x without using the built-in x \$\endgroup\$ Commented Jul 7, 2016 at 18:55
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    \$\begingroup\$ @PatrickRoberts Then whether the tag is appropriate boils down to "does this challenge allow built-ins," which seems similarly unnecessary. \$\endgroup\$
    – Alex A.
    Commented Jul 7, 2016 at 18:56
  • \$\begingroup\$ A challenge could disallow all built-ins, but in many cases that would render a language nearly or completely unusable. This tag is a little more sophisticated than whether a challenge allows built-ins or not. \$\endgroup\$ Commented Jul 7, 2016 at 19:14
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    \$\begingroup\$ I agree, I also think this would be a meta-tag. It doesn't seem to really describe anything about the challenge, only if the challenge has a rule about not using built-ins. This doesn't seem like a criteria that people would ever want to distinguish challenges on, or to search through challenges by. \$\endgroup\$ Commented Jul 7, 2016 at 20:20


This tag would remove confusion from many challenges where the asker does not know how to definitively say that "built-ins are allowed except for the built-in that implements what I'm asking you to", and we could have the tag wiki break down exactly what the rules are to prevent loopholes when wanting to post challenges that are particular about doing this in the spirit of reinventing the wheel.

For example, a challenge asks to implement an FFT. Okay, it's clear the asker forbids using a built-in FFT. But they didn't realize that a built-in DFT does not violate their restriction, and disregards the challenge's intention of reinventing the wheel. Using this tag as a way of saying that is also forbidden would make specifying challenge restrictions a lot easier.

  • \$\begingroup\$ On the contrary, I think it would be more confusing. It's both common and sufficient to state that built-ins which directly solve the challenge are banned. Things like that, especially things more complex than that, should be explicitly stated by the challenge author. Making a user read the tag wiki to figure out the rules of a challenge seems counterproductive. \$\endgroup\$
    – Alex A.
    Commented Jul 7, 2016 at 20:34

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