Current Config object have several issues.

1. User must not use zero-value. They should use NewConfig() instead.
2. New and old fields are coexists: tls and tlsConfig.
3. We have exposed Params map[string]string that makes fixing Is it possible to execute set variable sequentially? #1455 difficult.

The second problem will growth forever. We may add Compression bool and CompressionMethod []str later. To stop making Config bigger and more complex, I am considering two options:

Idea 1: Add methods to *Config

This is simpler approach. Keep existing Config fields but stop adding public fields anymore.
We will add methods to Config instead:

1. func (c *Config) SetCompression(enable bool)
2. func (c *Config) SetTimeTruncate(d time.Duration) (revert TimeTruncate field added recently but never released yet)

Example:

cfg := mysql.ParseDSN(dsn)
cfg.SetCompression(true)
cfg.SetTimeTruncate(time.Millisecond)

Idea 2: Use "Functional Option Pattern"

This is similar to the previous, but add one func (c *Config) SetOptions(option...) method instead of many Set***() methods and have many FOP functions like:

1. func Compression(enable bool) option
2. func TimeTruncate(d time.Duration) option

Example:

cfg := mysql.ParseDSN(dsn)
cfg.SetOptions(
 Compression(true),
 TimeTruncate(time.Millisecond),
)

Idea 1 is simpler. But with Idea 2, we can reuse option functions in new API and stop using Config completely like this:

// in the future...
connector, err := mysql.NewConnectorOptions(
 User("root"), Password("secret"),
 Host("mydb.local"),
 Database("myappdb"),
 Compression(true),
 TimeTruncate(time.Millisecond),
)

How do you think? @shogo82148, @arnehormann