From 8cb4e0cc38e2bf1ec596ae000caaf8e49c47dc31 Mon Sep 17 00:00:00 2001
From: Richard Lin
Date: Tue, 22 Nov 2016 00:57:12 -0800
Subject: Disallow chained apply (#380)

---
 .../src/main/scala/chisel3/core/package.scala        | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

(limited to 'chiselFrontend/src/main/scala/chisel3/core/package.scala')

diff --git a/chiselFrontend/src/main/scala/chisel3/core/package.scala b/chiselFrontend/src/main/scala/chisel3/core/package.scala
index 77f35c23..1d5817ae 100644
--- a/chiselFrontend/src/main/scala/chisel3/core/package.scala
+++ b/chiselFrontend/src/main/scala/chisel3/core/package.scala
@@ -16,14 +16,18 @@ package chisel3 {
     * after this call using apply, ie. 0.asUInt(1)(0) due to potential for
     * confusion (the 1 is a bit length and the 0 is a bit extraction position).
     * Prefer storing the result and then extracting from it.
+    *
+    * Implementation note: the empty parameter list (like `U()`) is necessary to prevent
+    * interpreting calls that have a non-Width parameter as a chained apply, otherwise things like
+    * `0.asUInt(16)` (instead of `16.W`) compile without error and produce undesired results.
     */
     implicit class fromBigIntToLiteral(val bigint: BigInt) {
       /** Int to UInt conversion, recommended style for constants.
         */
-      def U: UInt = UInt.Lit(bigint, Width())  // scalastyle:ignore method.name
+      def U(): UInt = UInt.Lit(bigint, Width())  // scalastyle:ignore method.name
       /** Int to SInt conversion, recommended style for constants.
         */
-      def S: SInt = SInt.Lit(bigint, Width())  // scalastyle:ignore method.name
+      def S(): SInt = SInt.Lit(bigint, Width())  // scalastyle:ignore method.name
       /** Int to UInt conversion with specified width, recommended style for constants.
         */
       def U(width: Width): UInt = UInt.Lit(bigint, width)  // scalastyle:ignore method.name
@@ -33,10 +37,10 @@ package chisel3 {
 
       /** Int to UInt conversion, recommended style for variables.
         */
-      def asUInt: UInt = UInt.Lit(bigint, Width())
+      def asUInt(): UInt = UInt.Lit(bigint, Width())
       /** Int to SInt conversion, recommended style for variables.
         */
-      def asSInt: SInt = SInt.Lit(bigint, Width())
+      def asSInt(): SInt = SInt.Lit(bigint, Width())
       /** Int to UInt conversion with specified width, recommended style for variables.
         */
       def asUInt(width: Width): UInt = UInt.Lit(bigint, width)
@@ -51,14 +55,14 @@ package chisel3 {
     implicit class fromStringToLiteral(val str: String) {
       /** String to UInt parse, recommended style for constants.
         */
-      def U: UInt = UInt.Lit(parse(str), parsedWidth(str))  // scalastyle:ignore method.name
+      def U(): UInt = UInt.Lit(parse(str), parsedWidth(str))  // scalastyle:ignore method.name
       /** String to UInt parse with specified width, recommended style for constants.
         */
       def U(width: Width): UInt = UInt.Lit(parse(str), width)  // scalastyle:ignore method.name
 
       /** String to UInt parse, recommended style for variables.
         */
-      def asUInt: UInt = UInt.Lit(parse(str), parsedWidth(str))
+      def asUInt(): UInt = UInt.Lit(parse(str), parsedWidth(str))
       /** String to UInt parse with specified width, recommended style for variables.
         */
       def asUInt(width: Width): UInt = UInt.Lit(parse(str), width)
@@ -88,11 +92,11 @@ package chisel3 {
     implicit class fromBooleanToLiteral(val boolean: Boolean) {
       /** Boolean to Bool conversion, recommended style for constants.
         */
-      def B: Bool = Bool.Lit(boolean)  // scalastyle:ignore method.name
+      def B(): Bool = Bool.Lit(boolean)  // scalastyle:ignore method.name
 
       /** Boolean to Bool conversion, recommended style for variables.
         */
-      def asBool: Bool = Bool.Lit(boolean)
+      def asBool(): Bool = Bool.Lit(boolean)
     }
 
     implicit class fromDoubleToLiteral(val double: Double) {
-- 
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