rework Get* methods with assertValue

Author: emar-kar

README.md

@@ -108,7 +108,6 @@ func main() {
 }
 ```
 Those functions triggered inside `ConfigParser.Get*` methods if presented and wraps the return value. 
-> NOTE: Since `ConvertFunc` returns `any`, the caller should guarantee type assertion to the requested type after custom processing!
 ```go
 type Converter map[string]ConvertFunc
 ```

methods.go

@@ -93,7 +93,7 @@ func (p *ConfigParser) Get(section, option string) (string, error) {
 		return "", err
 	}
 
-	return value.(string), nil
+	return assertValue[string](value)
 }
 
 func (p *ConfigParser) get(section, option string) (string, error) {
@@ -193,7 +193,7 @@ func (p *ConfigParser) GetInt64(section, option string) (int64, error) {
 		return 0, err
 	}
 
-	return value.(int64), nil
+	return assertValue[int64](value)
 }
 
 // GetFloat64 returns float64 representation of the named option.
@@ -212,7 +212,7 @@ func (p *ConfigParser) GetFloat64(section, option string) (float64, error) {
 		return 0, err
 	}
 
-	return value.(float64), nil
+	return assertValue[float64](value)
 }
 
 // GetBool returns bool representation of the named option.
@@ -231,7 +231,7 @@ func (p *ConfigParser) GetBool(section, option string) (bool, error) {
 		return false, err
 	}
 
-	return value.(bool), nil
+	return assertValue[bool](value)
 }
 
 // RemoveSection removes given section from the ConfigParser.
@@ -324,3 +324,16 @@ func defaultGetBool(value string) (any, error) {
 
 	return booleanValue, nil
 }
+
+// assertValue tries vakue assertuon to the given type, returns error if unsuccessful.
+func assertValue[T ~string | ~int64 | ~float64 | ~bool](value any) (T, error) {
+	v, ok := value.(T)
+	if ok {
+		return v, nil
+	}
+
+	// Default value of the type.
+	var d T
+
+	return d, fmt.Errorf("assertion to %T failed: incorrect value %q", d, value)
+}

methods_test.go

@@ -1,6 +1,8 @@
 package configparser_test
 
 import (
+	"strings"
+
 	"github.com/bigkevmcd/go-configparser"
 
 	gc "gopkg.in/check.v1"
@@ -368,3 +370,27 @@ func (s *ConfigParserSuite) TestOptionsWithSectionStripsWhitespaceFromKeys(c *gc
 	c.Assert(err, gc.IsNil)
 	c.Assert(result, gc.DeepEquals, []string{"base_dir", "bin_dir", "foo"})
 }
+
+func brokenConv(_ string) (any, error) { return nil, nil }
+
+// Get* methods must fail with a proper error instead of a panic if type assertion has failed.
+func (s *ConfigParserSuite) TestGetWithAssertionError(c *gc.C) {
+	parser, err := configparser.ParseReaderWithOptions(
+		strings.NewReader("[testing]\nstring=new string\nint=200\nfloat=3.14159265\nbool=TRUE"),
+		configparser.Converters(configparser.Converter{
+			configparser.StringConv: brokenConv,
+			configparser.IntConv:    brokenConv,
+			configparser.FloatConv:  brokenConv,
+			configparser.BoolConv:   brokenConv,
+		}),
+	)
+	c.Assert(err, gc.IsNil)
+	_, err = parser.Get("testing", "string")
+	c.Assert(err, gc.ErrorMatches, ".*assertion to string failed.*")
+	_, err = parser.GetInt64("testing", "int")
+	c.Assert(err, gc.ErrorMatches, ".*assertion to int64 failed.*")
+	_, err = parser.GetFloat64("testing", "float")
+	c.Assert(err, gc.ErrorMatches, ".*assertion to float64 failed.*")
+	_, err = parser.GetBool("testing", "bool")
+	c.Assert(err, gc.ErrorMatches, ".*assertion to bool failed.*")
+}

options.go

@@ -23,8 +23,6 @@ type options struct {
 }
 
 // Converter contains custom convert functions for available types.
-// The caller should guarantee type assertion to the requested type
-// after custom processing!
 type Converter map[int]ConvertFunc
 
 // Predefined types for Converter.