Add a coins_to_string helper

[maurolacy]

Move coins_to_string
https://github.com/confio/poe-contracts/blob/ab1b1b21d235ee08419a158e2f7b26be8057ec9d/contracts/tg4-stake/src/contract.rs#L478-L485

to cosmwasm-std (src/coins.rs).

[webmaster128]

I'm not super convinced we need this or should implement it here. In Cosmos SDK there is a dedicated Coins type which makes it easy to create helpers based on that. But lists of coins can create all sort of trouble, especially when it comes to duplicates and sorting. Creating coins_to_string opens more problems than it solves I think.

But I see two ways to improve the situation in the linked code:

1. A Coin has a display implementation that explicitely uses the Cosmos SDK formatting format!("{}{}", c.amount, c.denom).
2. The code only uses one coin

For this reason I think this is the more pragmatic and maybe even better solution:

diff --git a/contracts/tg4-stake/src/contract.rs b/contracts/tg4-stake/src/contract.rs
index 848f6b8..2f44b2a 100644
--- a/contracts/tg4-stake/src/contract.rs
+++ b/contracts/tg4-stake/src/contract.rs
@@ -461,29 +461,20 @@ pub fn execute_claim<Q: CustomQuery>(
     }
 
     let config = CONFIG.load(deps.storage)?;
-    let amount = coins(release.into(), config.denom);
+    let amount = coin(release.into(), config.denom);
 
     let res = Response::new()
         .add_attribute("action", "claim")
-        .add_attribute("tokens", coins_to_string(&amount))
+        .add_attribute("tokens", amount.to_string())
         .add_attribute("sender", &info.sender)
         .add_message(BankMsg::Send {
             to_address: info.sender.into(),
-            amount,
+            amount: vec![amount],
         });
 
     Ok(res)
 }
 
-// TODO: put in cosmwasm-std (https://github.com/CosmWasm/cosmwasm/issues/1359)
-fn coins_to_string(coins: &[Coin]) -> String {
-    let strings: Vec<_> = coins
-        .iter()
-        .map(|c| format!("{}{}", c.amount, c.denom))
-        .collect();
-    strings.join(",")
-}
-
 #[cfg_attr(not(feature = "library"), entry_point)]
 pub fn sudo(
     deps: DepsMut<TgradeQuery>,

[webmaster128]

Closing in favour of #1377