go-tour: add Type Inference and Zero Values slides
Also check off a couple of finished things from the TODO list.
LGTM=campoy
R=campoy, golang-codereviews
CC=golang-codereviews
https://golang.org/cl/116090043
diff --git a/TODO b/TODO
index 3a8ffe8..ec4fa3d 100644
--- a/TODO
+++ b/TODO
@@ -15,8 +15,9 @@
* Variables with initializers
* Short variable declarations
* Basic types
+* Type inference
* Type conversions
-- The zero value
+* Zero values
* Constants
* Numeric Constants
* For
@@ -36,7 +37,7 @@
* Slices
* Slicing slices
* Making slices
-- Append
+* Append
- Copy
* Nil slices
* Range
@@ -90,7 +91,7 @@
* Exercise: Equivalent Binary Trees
* Exercise: Web Crawler
- More language features
-- Defer
+* Defer
- Panic and recover
- init functions
- Tools
diff --git a/content/basics.article b/content/basics.article
index e620aa6..a3e345a 100644
--- a/content/basics.article
+++ b/content/basics.article
@@ -142,6 +142,18 @@
.play basics/basic-types.go
+* Zero values
+
+Variables declared without an explicit initial value are given their
+_zero_value_.
+
+The zero value is:
+- `0` for numeric types,
+- `false` the boolean type, and
+- `""` (the empty string) for strings.
+
+.play basics/zero.go
+
* Type conversions
The expression `T(v)` converts the value `v` to the type `T`.
@@ -164,6 +176,25 @@
.play basics/type-conversions.go
+* Type inference
+
+When declaring a variable without specifying its type (using `var` without a type or the `:=` syntax), the variable's type is _inferred_ from the value on the right hand side.
+
+When the right hand side of the declaration is typed, the new variable is of that same type:
+
+ var i int
+ j := i // j is an int
+
+But when the right hand side contains an untyped numeric constant, the new variable may be an `int`, `float64`, or `complex128` depending on the precision of the constant:
+
+ i := 42 // int
+ f := 3.142 // float64
+ g := 0.867 + 0.5i // complex128
+
+Try changing the initial value of `v` in the example code and observe how its type is affected.
+
+.play basics/type-inference.go
+
* Constants
Constants are declared like variables, but with the `const` keyword.
diff --git a/content/basics/type-inference.go b/content/basics/type-inference.go
new file mode 100644
index 0000000..1db8ace
--- /dev/null
+++ b/content/basics/type-inference.go
@@ -0,0 +1,8 @@
+package main
+
+import "fmt"
+
+func main() {
+ v := 42 // change me!
+ fmt.Printf("v is of type %T\n", v)
+}
diff --git a/content/basics/zero.go b/content/basics/zero.go
new file mode 100644
index 0000000..9a391c9
--- /dev/null
+++ b/content/basics/zero.go
@@ -0,0 +1,11 @@
+package main
+
+import "fmt"
+
+func main() {
+ var i int
+ var f float64
+ var b bool
+ var s string
+ fmt.Printf("%v %v %v %q\n", i, f, b, s)
+}
