Usage of "You're welcome, etc..."

“Thank you.”
“You’re welcome.”

“I didn’t hear you enter.”
“The door was open.”

Now we get to my problem. I often use “dispose” when programming, and check if various objects in my program are disposed. There are probably similar cases when this happens, but I couldn’t think of any from the top of my head.

“Can you check the connection?”
“The connection is open.”
“Can you check the state of the object?”
“The object is disposed.”

How come here we use “disposed” instead of “dispose”? What am I missing?

I think i got an easier example:

“The shop is open during the workdays and closed during the weekend.”

So, why isn’t it “close” during the weekend and “opened” otherwise? (except the fact that it sounds wrong) Can someone explain the rule to me, or are these exceptions?

It seems to me that word open is an adjective in the sentence and describes the state of the door. “The door was open”.

“Open” is an adjective.
“Closed” is also an adjective.

They’re spelled differently, and the latter seems to be derived from the past participle of the verb “to close.” Participles are verbs acting as adjectives, and adjectives that began as participles would tend to look like “closed” or “annoying.”

The singing bird was adored by the crowd.

“Singing” - present participle acting as adj.

How do I know? Because I can do this:

The bird is singing. (Use it in the progressive tenses as a verb.)
The problem, once solved, began anew.

“Solved” - past participle acting as adj.

How do I know? Because I can do this:

This problem has been solved. (Use it in the perfect tenses as a verb.)

These two examples are not listed in dictionaries as adjectives, but you see that they can easily be used that way. That is the nature of participles.

Note that you could never say something was “close” if you mean it is “closed.” “Close” is an adjective meaning “near.”

“Disposed” is an adjective when it means “inclined.”

“Dispose” is just a verb.

Participles routinely act as adjectives, and some enter the dictionary as adjectives themselves once they’re ubiquitous in that form. They will still resemble the verbs they were taken from.

Other genuine adjectives derived from participles:

You could say the door is “opened,” but it sounds a bit absurd or unnecessary since we already have a proper adjective to convey that.

Sometimes we still use participles when we have proper adjectives that perform the desired function:

I found him impressing. - Participle as adj.
I found him impressive. - Adj.

What I’m asking, I guess, is how can I be sure I’m using the correct word? I mean, in “You’re welcome.” and “The doors were open.” it’s clear, because those examples are often used.

But, for example (and it’s probably a bad example):
“When we got to the seaside, my friend was already tan.” – or is it tanned?

Or, again, when I encounter some strange word in programming:
“The code was obfuscate.” – does this properly serve as an adjective, is the sentence gramatically correct? (if yes, it would mean something like: “Your program was hard to read.”) Here, “obfuscated” would change the meaning into “The process of obfuscation was performed on the code.”

“Tan” or “tanned” could work there. It’s not going to be wrong in any context. The meaning will come out the same.

As for your “obfuscate” example, if you know for sure the meaning is different from the past participle, choose the appropriate form. That’s technical language. Do what’s correct in that context.

If the meaning is the same, then you have no problem.

He is sophisticate.
He is sophisticated.

Same meaning.