Get rid of core::string in sr-std. (#783)

substrate/srml/contract/src/vm/env_def/macros.rs

@@ -280,6 +280,6 @@ mod tests {
 		);
 
 		let env = init_env::<MockExt>();
-		assert!(env.funcs.get("ext_gas").is_some());
+		assert!(env.funcs.get(&b"ext_gas"[..]).is_some());
 	}
 }

substrate/srml/contract/src/vm/env_def/mod.rs

@@ -18,7 +18,6 @@ use super::{SpecialTrap, BalanceOf, CreateReceipt, Ext, GasMeterResult, Runtime}
 use codec::{Encode, Decode};
 use parity_wasm::elements::{FunctionType, ValueType};
 use rstd::prelude::*;
-use rstd::string::String;
 use rstd::collections::btree_map::BTreeMap;
 use runtime_primitives::traits::{As, CheckedMul};
 use sandbox::{self, TypedValue};
@@ -75,7 +74,7 @@ impl ConvertibleToWasm for u64 {
 /// which can be imported and called by the module.
 pub(crate) struct HostFunctionSet<E: Ext> {
 	/// Functions which defined in the environment.
-	pub funcs: BTreeMap<String, HostFunction<E>>,
+	pub funcs: BTreeMap<Vec<u8>, HostFunction<E>>,
 }
 impl<E: Ext> HostFunctionSet<E> {
 	pub fn new() -> Self {

substrate/srml/contract/src/vm/prepare.rs

@@ -138,7 +138,7 @@ impl<'a, T: Trait> ContractModule<'a, T> {
 
 			let ext_func = env
 				.funcs
-				.get(import.field())
+				.get(import.field().as_bytes())
 				.ok_or_else(|| Error::Instantiate)?;
 			if !ext_func.func_type_matches(func_ty) {
 				return Err(Error::Instantiate);