Improve request typing

packages/truffle-debugger/lib/data/sagas/index.js

@@ -65,13 +65,15 @@ export function* decode(definition, ref) {
   while (!result.done) {
     let request = result.value;
     let response;
-    switch (request.requesting) {
+    switch (request.type) {
       //yes, this is a little silly right now
       case "storage":
         //the debugger supplies all storage it knows at the beginning.
         //any storage it does not know is presumed to be zero.
         response = ZERO_WORD;
         break;
+      default:
+        debug("unrecognized request type!");
     }
     result = decoder.next(response);
   }

packages/truffle-decoder/lib/interface/contract-decoder.ts

@@ -12,7 +12,7 @@ import * as storage from "../allocate/storage";
 import { StoragePointer, isStoragePointer } from "../types/pointer";
 import { StorageAllocations, StorageMemberAllocations, StorageMemberAllocation } from "../types/allocation";
 import { Slot, isWordsLength } from "../types/storage";
-import { DecoderRequest } from "../types/request";
+import { DecoderRequest, isStorageRequest } from "../types/request";
 import decode from "../decode";
 import { Definition as DefinitionUtils, EVM, AstDefinition, AstReferences } from "truffle-decode-utils";
 import { BlockType, Transaction } from "web3/eth/types";
@@ -178,17 +178,16 @@ export default class TruffleContractDecoder extends AsyncEventEmitter {
     while(!result.done) {
       let request = <DecoderRequest>(result.value);
       let response: any
-      switch(request.requesting) {
-        //yes, this is a little silly right now
-        case "storage":
-          response = DecodeUtils.Conversion.toBytes(
-            await this.web3.eth.getStorageAt(
-              this.contractAddress,
-              request.slot,
-              block),
-            DecodeUtils.EVM.WORD_SIZE);
-          break;
+      if(isStorageRequest(request)) {
+        response = DecodeUtils.Conversion.toBytes(
+          await this.web3.eth.getStorageAt(
+            this.contractAddress,
+            request.slot,
+            block),
+          DecodeUtils.EVM.WORD_SIZE);
       }
+      //note: one of the above conditionals *must* be true by the type system.
+      //yes, right now there's only one such conditional.
       result = decoder.next(response);
     }
     //at this point, result.value holds the final value

packages/truffle-decoder/lib/read/storage.ts

@@ -73,7 +73,7 @@ export function* read(storage: WordMapping, slot: Slot): IterableIterator<Uint8A
   //say 0)
   if(word === undefined) {
     word = yield {
-      requesting: "storage",
+      type: "storage",
       slot: address
     };
   }

packages/truffle-decoder/lib/types/request.ts

@@ -1,6 +1,12 @@
 import BN from "bn.js";
 
-export interface DecoderRequest {
-  requesting: "storage";
-  slot?: BN; //will add more fields as needed
+export type DecoderRequest = StorageRequest; //will add more later
+
+export interface StorageRequest {
+  type: "storage";
+  slot: BN; //will add more fields as needed
+}
+
+export function isStorageRequest(request: DecoderRequest): request is StorageRequest {
+  return request.type === "storage";
 }