重構指南 - 分解複雜判斷（Remove Arrowhead Antipattern）

當代碼中有多層嵌套時，會降低代碼的可讀性，對於以後的修改也增加難度，所以我們需要分解複雜的判斷並儘快返回。

重構前代碼

public class Security
{
    public ISecurityChecker SecurityChecker { get; set; }

    public Security(ISecurityChecker securityChecker)
    {
        SecurityChecker = securityChecker;
    }

    public bool HasAccess(User user, Permission permission, IEnumerable<Permission> exemptions)
    {
        bool hasPermission = false;

        if (user != null)
        {
            if (permission != null)
            {
                if (exemptions.Count() == 0)
                {
                    if (SecurityChecker.CheckPermission(user, permission) || exemptions.Contains(permission))
                    {
                        hasPermission = true;
                    }
                }
            }
        }

        return hasPermission;
    }
}

重構後代碼

public class Security
{
    public ISecurityChecker SecurityChecker { get; set; }

    public Security(ISecurityChecker securityChecker)
    {
        SecurityChecker = securityChecker;
    }

    public bool HasAccess(User user, Permission permission, IEnumerable<Permission> exemptions)
    {
        if (user == null || permission == null)
            return false;

        if (exemptions.Contains(permission))
            return true;

        return SecurityChecker.CheckPermission(user, permission);
    }
}

重構後的代碼，大大提高了可讀性和以後的可維護性。