Add some explaining comments

Author: odersky

compiler/src/dotty/tools/dotc/core/Names.scala

@@ -11,6 +11,7 @@ import scala.internal.Chars.isIdentifierStart
 import collection.immutable
 import config.Config
 import java.util.HashMap
+import Contexts.{Context, ctx}
 
 import scala.annotation.internal.sharable
 
@@ -638,12 +639,18 @@ object Names {
   def typeName(bs: Array[Byte], offset: Int, len: Int): TypeName =
     termName(bs, offset, len).toTypeName
 
-  /** Create a term name from a string, without encoding operators */
+  /** Create a term name from a string.
+   *  See `termName(s: String, from: Int, len: Int) for a more efficient version
+   *  which however requires a Context for its operation
+   */
   def termName(s: String): SimpleName = termName(s.toCharArray, 0, s.length)
 
-  /** Create a type name from a string, without encoding operators */
+  /** Create a type name from a string */
   def typeName(s: String): TypeName = typeName(s.toCharArray, 0, s.length)
 
+  /** Create a term name from a string slice, using a common buffer.
+   *  This avoids some allocation relative to `termName(s: String)`
+   */
   def termName(s: String, from: Int, len: Int)(using ctx: Contexts.Context): TermName = {
     val base = ctx.base
 
@@ -654,7 +661,10 @@ object Names {
     termName(base.nameCharBuffer, 0, len)
   }
 
-  def typeName(s: String, from: Int, len: Int)(using ctx: Contexts.Context): TypeName =
+  /** Create a type name from a string slice, using a common buffer.
+   *  This avoids some allocation relative to `typeName(s: String)`
+   */
+  def typeName(s: String, from: Int, len: Int)(using Context): TypeName =
     termName(s, from, len).toTypeName
 
   table(0) = new SimpleName(-1, 0, null)