diff options
Diffstat (limited to 'doc/go_tutorial.txt')
| -rw-r--r-- | doc/go_tutorial.txt | 19 |
1 files changed, 12 insertions, 7 deletions
diff --git a/doc/go_tutorial.txt b/doc/go_tutorial.txt index 76dba34ef..6ab6094c0 100644 --- a/doc/go_tutorial.txt +++ b/doc/go_tutorial.txt @@ -622,13 +622,18 @@ We've seen simple uses of the package "fmt", which implements "Printf", "Fprintf", and so on. Within the "fmt" package, "Printf" is declared with this signature: - Printf(format string, v ...) (n int, errno os.Error) - -That "..." represents the variadic argument list that in C would -be handled using the "stdarg.h" macros but in Go is passed using -an empty interface variable ("interface {}") and then unpacked -using the reflection library. It's off topic here but the use of -reflection helps explain some of the nice properties of Go's "Printf", + Printf(format string, v ...interface{}) (n int, errno os.Error) + +The token "..." introduces a variable-length argument list that in C would +be handled using the "stdarg.h" macros. +In Go, variadic functions are passed a slice of the arguments of the +specified type. In "Printf"'s case, the declaration says "...interface{}" +so the actual type is a slice of empty interface values, "[]interface{}". +"Printf" can examine the arguments by iterating over the slice +and, for each element, using a type switch or the reflection library +to interpret the value. +It's off topic here but such run-time type analysis +helps explain some of the nice properties of Go's "Printf", due to the ability of "Printf" to discover the type of its arguments dynamically. |