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<h1> Package printer </h1> <ul id="short-nav">
<li><code>import "go/printer"</code></li>
<li><a href="#pkg-overview" class="overviewLink">Overview</a></li>
<li><a href="#pkg-index" class="indexLink">Index</a></li>
<li><a href="#pkg-examples" class="examplesLink">Examples</a></li>
</ul> <h2 id="pkg-overview">Overview </h2> <p>Package printer implements printing of AST nodes. </p> <h2 id="pkg-index">Index </h2> <ul id="manual-nav">
<li><a href="#Fprint">func Fprint(output io.Writer, fset *token.FileSet, node any) error</a></li>
<li><a href="#CommentedNode">type CommentedNode</a></li>
<li><a href="#Config">type Config</a></li>
<li> <a href="#Config.Fprint">func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node any) error</a>
</li>
<li><a href="#Mode">type Mode</a></li>
</ul> <div id="pkg-examples"> <h3>Examples</h3> <dl> <dd><a class="exampleLink" href="#example_Fprint">Fprint</a></dd> </dl> </div> <h3>Package files</h3> <p> <span>comment.go</span> <span>gobuild.go</span> <span>nodes.go</span> <span>printer.go</span> </p> <h2 id="Fprint">func <span>Fprint</span> </h2> <pre data-language="go">func Fprint(output io.Writer, fset *token.FileSet, node any) error</pre> <p>Fprint "pretty-prints" an AST node to output. It calls <a href="#Config.Fprint">Config.Fprint</a> with default settings. Note that gofmt uses tabs for indentation but spaces for alignment; use format.Node (package go/format) for output that matches gofmt. </p> <h4 id="example_Fprint"> <span class="text">Example</span>
</h4> <p>Code:</p> <pre class="code" data-language="go">package printer_test
import (
"bytes"
"fmt"
"go/ast"
"go/parser"
"go/printer"
"go/token"
"strings"
)
func parseFunc(filename, functionname string) (fun *ast.FuncDecl, fset *token.FileSet) {
fset = token.NewFileSet()
if file, err := parser.ParseFile(fset, filename, nil, 0); err == nil {
for _, d := range file.Decls {
if f, ok := d.(*ast.FuncDecl); ok && f.Name.Name == functionname {
fun = f
return
}
}
}
panic("function not found")
}
func printSelf() {
// Parse source file and extract the AST without comments for
// this function, with position information referring to the
// file set fset.
funcAST, fset := parseFunc("example_test.go", "printSelf")
// Print the function body into buffer buf.
// The file set is provided to the printer so that it knows
// about the original source formatting and can add additional
// line breaks where they were present in the source.
var buf bytes.Buffer
printer.Fprint(&buf, fset, funcAST.Body)
// Remove braces {} enclosing the function body, unindent,
// and trim leading and trailing white space.
s := buf.String()
s = s[1 : len(s)-1]
s = strings.TrimSpace(strings.ReplaceAll(s, "\n\t", "\n"))
// Print the cleaned-up body text to stdout.
fmt.Println(s)
}
func ExampleFprint() {
printSelf()
// Output:
// funcAST, fset := parseFunc("example_test.go", "printSelf")
//
// var buf bytes.Buffer
// printer.Fprint(&buf, fset, funcAST.Body)
//
// s := buf.String()
// s = s[1 : len(s)-1]
// s = strings.TrimSpace(strings.ReplaceAll(s, "\n\t", "\n"))
//
// fmt.Println(s)
}
</pre> <h2 id="CommentedNode">type <span>CommentedNode</span> </h2> <p>A CommentedNode bundles an AST node and corresponding comments. It may be provided as argument to any of the <a href="#Fprint">Fprint</a> functions. </p>
<pre data-language="go">type CommentedNode struct {
Node any // *ast.File, or ast.Expr, ast.Decl, ast.Spec, or ast.Stmt
Comments []*ast.CommentGroup
}
</pre> <h2 id="Config">type <span>Config</span> </h2> <p>A Config node controls the output of Fprint. </p>
<pre data-language="go">type Config struct {
Mode Mode // default: 0
Tabwidth int // default: 8
Indent int // default: 0 (all code is indented at least by this much); added in Go 1.1
}
</pre> <h3 id="Config.Fprint">func (*Config) <span>Fprint</span> </h3> <pre data-language="go">func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node any) error</pre> <p>Fprint "pretty-prints" an AST node to output for a given configuration cfg. Position information is interpreted relative to the file set fset. The node type must be *<span>ast.File</span>, *<a href="#CommentedNode">CommentedNode</a>, []<span>ast.Decl</span>, []<span>ast.Stmt</span>, or assignment-compatible to <span>ast.Expr</span>, <span>ast.Decl</span>, <span>ast.Spec</span>, or <span>ast.Stmt</span>. </p>
<h2 id="Mode">type <span>Mode</span> </h2> <p>A Mode value is a set of flags (or 0). They control printing. </p>
<pre data-language="go">type Mode uint</pre> <pre data-language="go">const (
RawFormat Mode = 1 << iota // do not use a tabwriter; if set, UseSpaces is ignored
TabIndent // use tabs for indentation independent of UseSpaces
UseSpaces // use spaces instead of tabs for alignment
SourcePos // emit //line directives to preserve original source positions
)</pre><div class="_attribution">
<p class="_attribution-p">
© Google, Inc.<br>Licensed under the Creative Commons Attribution License 3.0.<br>
<a href="http://golang.org/pkg/go/printer/" class="_attribution-link">http://golang.org/pkg/go/printer/</a>
</p>
</div>
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