Merge pull request #5836 from trufflesuite/contract-docs

add blurb in @truffle/contract README about overloaded functions

Author: eggplantzzz

packages/contract/README.md

@@ -240,11 +240,11 @@ contract MyContract {
 }
 ```
 
-From Javascript's point of view, this contract has three functions: `setValue`, `getValue` and `value`. This is because `value` is public and automatically creates a getter function for it.
+From JavaScript's point of view, this contract has three functions: `setValue`, `getValue` and `value`. This is because `value` is public and automatically creates a getter function for it.
 
 #### Making a transaction via a contract function
 
-When we call `setValue()`, this creates a transaction. From Javascript:
+When we call `setValue()`, this creates a transaction. From JavaScript:
 
 ```javascript
 const result = instance.setValue(5);
@@ -310,6 +310,80 @@ const val = instance.getValue();
 // since the contract returns that value.
 ```
 
+#### Overloaded functions
+
+Solidity supports a contract having multiple functions with the same name as long as the
+function argument types differ. And so you may find yourself in the situation of having a
+Truffle contract object with this property.
+You can invoke these "overloaded" functions just like you would a normal contract function. Truffle contract instances
+actually wrap web3's contract abstraction (`web3.eth.Contract`) and when you call an overloaded function, it
+uses the same function resolution that web3 uses. However, we must give a warning that this overloaded function
+resolution is often imprecise and can resolve to the wrong function when you call it.
+
+Consider the following contrived code sample:
+
+```solidity
+contract MyContract {
+  uint256 public myUint;
+  string public myString;
+  string public myOtherString;
+
+  function setValues(uint256 val, string str) {
+    myUint = val;
+    myString = str
+  }
+
+  function setValues(string str, string otherStr) {
+    myString = str;
+    myOtherString = otherStr;
+  }
+
+  function setValues(uint256 val, string str, string otherStr) {
+    myUint = val;
+    myString = str;
+    myOtherString = otherStr;
+  }
+}
+```
+
+This Solidity contract contains three functions named `setValues`, each taking a different type of input. In your JavaScript you
+might do something like the following:
+
+```javascript
+await instance.setValue(
+  666,
+  "this is not string cheese",
+  "this is string cheese"
+);
+```
+
+As mentioned above, Truffle contract wraps web3 `Contract` objects and uses web3's overloaded function resolution.
+To resolve these functions, web3's strategy is to look at the number of arguments that the function was invoked with and try
+one that takes that many arguments. This works for some cases but is not ideal in that it
+can invoke the incorrect function. Take, for example, the case where we do something like the following:
+
+```javascript
+await instance.setValue("this is not string cheese", "this is string cheese");
+```
+
+We know that in our contract there are two functions named `setValues` that take
+two arguments. In the above case, we cannot be sure whether web3's resolution will resolve to the first or second
+function. The more precise way to reference functions like this is to use
+the `methods` property on the contract instance. The following is an example of how you
+access these methods:
+
+```javascript
+await instance.methods["setValue(string,string)"](
+  "this is not string cheese",
+  "this is string cheese"
+);
+```
+
+The `methods` property is an object whose keys are strings that correspond to the contract function's names
+and signatures with no spaces. The values are the functions themselves. You can inspect the
+`methods` property to see the key names in this object and match the function signature.
+We recommend using this method of calling overloaded functions since it will unambiguously resolve to the correct function.
+
 #### Processing transaction results
 
 When you make a transaction, you're given a `result` object that gives you a wealth of information about the transaction. You're given the transaction hash (`result.tx`), the decoded events (also known as logs; `result.logs`), and a transaction receipt (`result.receipt`). In the below example, you'll receive the `ValueSet()` event because you triggered the event using the `setValue()` function: