Add payment-channel example

[kanishkatn]

I've been working on implementing payment-channel contract and felt it could go into the examples here. I've basically implemented it by referring to this post which does it in Solidity.

This is my first PR. I've followed the contributing guidelines. Happy to make any changes if needed.

[HCastano]

@kanishkatn thanks for your PR! I'll try and spend some time this week on it 😃

[HCastano]

Good start!

I haven't gone through everything just yet, but I think there's enough comments to get you going before I circle back to this.

A few other things

• You should merge master into your branch, there's been a few changes since you opened this (sorry about that!)
• Instead of panic!-ing, try returning Result's
  • This is more idiomatic Rust, and also allows for more ergonomic error handling from the perspective of other contracts as well as UIs

[kanishkatn]

@HCastano Thank you for taking the time to review it. I'll make the changes in a day or two

[kanishkatn]

Hi @HCastano , thanks for waiting. I have made the changes.

Regarding replacing panic with Result, I couldn't do it in the messages that terminates the contract. The method ink_env::test::assert_contract_termination used in tests, expects the function to return () and wasn't compiling for Result<()>. I couldn't find a way around it.

[paritytech-cicd-pr]

🦑 📈 ink! Example Contracts ‒ Changes Report 📉 🦑

These are the results when building the examples/* contracts from this branch with cargo-contract 1.4.0-25bfb96 and comparing them to ink! master:

	Δ Optimized Size	Δ Used Gas	Total Optimized Size	Total Used Gas
accumulator			1.00 K
adder			2.04 K
contract-introspection			2.32 K
contract-terminate			0.92 K	275_000
contract-transfer			8.31 K	75_000
data-structures			1.73 K
delegate-calls			2.89 K	76_242
delegator			6.34 K	232_136
dns			8.81 K	225_000
erc1155			16.74 K	450_000
erc20			8.42 K	225_000
erc721			11.62 K	600_000
flipper			1.24 K	75_000
forward-calls			2.87 K	151_411
incrementer			1.14 K
mother			12.16 K
multisig			25.28 K	470_240
payment-channel	+7.95 K		7.95 K
rand-extension			3.79 K	75_000
seal-code-hash			1.39 K
seal-ecdsa			1.71 K
set-code-hash			1.49 K	150_000
subber			2.06 K
trait-erc20			8.69 K	225_000
trait-flipper			0.97 K	75_000
trait-incrementer			1.12 K	150_000
updated-incrementer			9.72 K
upgradeable-flipper			1.48 K

Link to the run | Last update: Sat Jul 2 05:09:47 CEST 2022

[HCastano]

I'll slowly keep chipping away at this, sorry for taking so long!

[HCastano]

Thanks for adding this. Can you also wrap everything here to 90 characters?

[kanishkatn]

It's done.

[kanishkatn]

@HCastano No rush. I've been a bit swamped at work as well.

I've resolved all the changes mentioned in the review comments. I'm learning so much from this. Thank you!

[kanishkatn]

Hey @HCastano , could we merge this? I believe it's ready to go in!

[HCastano]

Hey @HCastano , could we merge this? I believe it's ready to go in!

Let me take another look at this PR this week 🔎

[HCastano]

Some small things left, but I think we can merge soon!

[kanishkatn]

I've made the changes. It's looking so clean now!!

[HCastano]

Thanks for adding this example! Sorry it took so long.

The CI failures aren't related to your code, we've been having some issues with our pipelines recently. So if we don't merge this it's because we're waiting on the CI fixes

[kanishkatn]

Thank you for your time @HCastano !