| Index: doc/effective_go.html |
| =================================================================== |
| --- a/doc/effective_go.html |
| +++ b/doc/effective_go.html |
| @@ -1121,9 +1121,23 @@ |
| <p> |
| Assigning and fetching map values looks syntactically just like |
| doing the same for arrays except that the index doesn't need to |
| -be an integer. An attempt to fetch a map value with a key that |
| -is not present in the map will cause the program to crash, but |
| -there is a way to do so safely using a multiple assignment. |
| +be an integer. |
| +</p> |
| +<pre> |
| +offset := timeZone["EST"] |
| +</pre> |
| +<p> |
| +An attempt to fetch a map value with a key that |
| +is not present in the map will return the zero value for the type |
| +of the entries |
| +in the map. For instance, if the map contains integers, looking |
| +up a non-existent key will return <code>0</code>. |
| +</p> |
| +<p> |
| +Sometimes you need to distinguish a missing entry from |
| +a zero value. Is there an entry for <code>"UTC"</code> |
| +or is that zero value because it's not in the map at all? |
| +You can discriminate with a form of multiple assignment. |
| </p> |
| <pre> |
| var seconds int |
| @@ -1136,7 +1150,7 @@ |
| will be set appropriately and <code>ok</code> will be true; if not, |
| <code>seconds</code> will be set to zero and <code>ok</code> will |
| be false. |
| -Here's a function that puts it together: |
| +Here's a function that puts it together with a nice error report: |
| </p> |
| <pre> |
| func offset(tz string) int { |
| @@ -1151,7 +1165,7 @@ |
| To test for presence in the map without worrying about the actual value, |
| you can use the <em>blank identifier</em>, a simple underscore (<code>_</code>). |
| The blank identifier can be assigned or declared with any value of any type, with the |
| -value discarded harmlessly. For testing presence in a map, use the blank |
| +value discarded harmlessly. For testing just presence in a map, use the blank |
| identifier in place of the usual variable for the value. |
| </p> |
| <pre> |
| @@ -1166,6 +1180,7 @@ |
| <pre> |
| timeZone["PDT"] = 0, false // Now on Standard Time |
| </pre> |
| + |
| <h3 id="printing">Printing</h3> |
| <p> |
